These items of business are described in the accompanying joint proxy statement/prospectus, which we encourage you to read in its entirety before voting.

Only holders of record of GPIA ordinary shares at the close of business on [•], 2017 are entitled to notice of and to vote and have their votes counted at the extraordinary general meeting and any adjournment of the extraordinary general meeting.

We are providing the accompanying joint proxy statement/prospectus and accompanying proxy card to our shareholders in connection with the solicitation of proxies to be voted at the extraordinary general meeting and at any adjournment of the extraordinary general meeting. Whether or not you plan to attend the extraordinary general meeting, we urge you to read the accompanying joint proxy statement/prospectus (and any documents incorporated into the accompanying joint proxy statement/prospectus by reference) carefully. Please pay particular attention to the section entitled “ Risk Factors ”.

After careful consideration, GPIA’s board of directors has determined that the business combination proposal, the domestication proposal, each of the organizational documents proposals, the stock issuance proposal and the adjournment proposal are in the best interests of GPIA and its shareholders and unanimously recommends that you vote or give instruction to vote “FOR” each of those proposals.

The existence of financial and personal interests of one or more of GPIA’s directors may result in a conflict of interest on the part of such director(s) between what he or they may believe is in the best interests of GPIA and its shareholders and what he or they may believe is best for himself or themselves in determining to recommend that shareholders vote for the proposals. See the section entitled “ GPIA Business Combination Proposal—Interests of GPIA’s Directors and Officers in the Business Combination ” in the accompanying joint proxy statement/prospectus for a further discussion of this.

Under the merger agreement, the approval of the condition precedent proposals is a condition to the consummation of the first merger. The domestication proposal is conditioned on the approval of the business combination proposal. The organizational documents proposals are conditioned on the approval of the domestication proposal, and, therefore, also conditioned on approval of the business combination proposal. The stock issuance proposal is conditioned on the approval of the organizational documents proposals, and, therefore, also conditioned on approval of the domestication proposal and the business combination proposal. The adjournment proposal is not conditioned on the approval of any other proposal. If our public shareholders do not approve each of the condition precedent proposals, then unless this condition is waived by GPIA, Let’s Go and Rimini Street, the merger agreement could terminate and the proposed business combination may not be consummated. In addition, the amendment, modification or waiver of the merger agreement in any manner that could reasonably be expected to be materially adverse to Rimini Street or the agents and lenders under the Credit Facility (as described in the accompanying joint proxy statement/prospectus) requires the prior written consent of the Origination Agent thereunder. There can be no assurance that GPIA, Let’s Go and Rimini Street would waive any such provision of the merger agreement, or that the agents and lenders under the Credit Facility would provide any required consents to such amendments, modifications or waivers.

In connection with our initial public offering, our initial shareholders (consisting of the Sponsor and our independent directors at the time of our initial public offering) entered into letter agreements to vote their founder shares, as well as any public shares purchased during or after our initial public offering, in favor of the business combination proposal. In addition, on May 16, 2017, in connection with the transactions contemplated by the merger agreement, GPIAC, LLC, a company whose sole member is the Sponsor (“GPIAC, LLC”) entered into a transaction support and voting agreement with GPIA and Rimini Street, pursuant to which, among other things, GPIAC, LLC agreed to vote its GPIA ordinary shares in favor of the transactions at the extraordinary general meeting. As of the date of this joint proxy statement/prospectus, the aggregate number of shares covered by the transaction support and voting agreement entered into by GPIAC, LLC represents 21.3% of the outstanding GPIA ordinary shares. In addition, our independent directors have indicated that they intend to vote their shares in favor of all other proposals being presented at the extraordinary general meeting. As of the date of this joint proxy statement/prospectus, our independent directors own 0.3% of the outstanding GPIA ordinary shares.

Pursuant to our memorandum and articles of association, a public shareholder may request of GPIA that RMNI redeem all or a portion of the RMNI public shares that such public shareholder will hold upon the domestication for cash if the business combination is consummated. For the purposes of Article 48.3 of our memorandum and articles of association and the Cayman Islands Companies Law (2016 Revision), the exercise of redemption rights shall be treated as an election to have such public shares repurchased for cash and references in this joint proxy statement/prospectus to “redemption” or “redeeming” shall be interpreted accordingly. GP Investments Acquisition Corp. (after its domestication as a corporation incorporated in the State of Delaware) will be the continuing entity following the domestication, which is the entity that survives the mergers (and which will be renamed “Rimini Street, Inc.” immediately after consummation of the second merger). As a change of entity name does not involve a change

in the legal form of the entity, in this joint proxy statement/prospectus, “RMNI” refers to GP Investments Acquisition Corp. (after its domestication as a corporation incorporated in the State of Delaware), including subsequent to its change of name to Rimini Street, Inc. Holders of GPIA public shares will be entitled to receive cash for any RMNI public shares to be redeemed only if you:

Holders of GPIA public shares should complete the procedures for electing to redeem their GPIA public shares in the manner described above prior to 5:00 p.m. Eastern Time on [ • ], 2017 (two business days before the extraordinary general meeting).

Holders of units must elect to separate the underlying public shares and public warrants prior to exercising redemption rights with respect to the public shares. If holders hold their units in an account at a brokerage firm or bank, holders must notify their broker or bank that they elect to separate the units into the underlying public shares and public warrants, or if a holder holds units registered in its own name, the holder must contact Continental Stock Transfer & Trust Company, GPIA’s transfer agent, directly and instruct them to do so. Public stockholders may elect to redeem RMNI public shares regardless of if or how they vote in respect of the business combination proposal. If the business combination is not consummated, the public shares will not be redeemed for cash. If a public shareholder properly exercises its right to redeem all or a portion of the RMNI public shares that it will hold upon the domestication and timely delivers its shares to Continental Stock Transfer & Trust Company, GPIA’s transfer agent, RMNI will redeem such RMNI public shares into a pro rata portion of the trust account established at the consummation of our initial public offering, calculated as of two business days prior to the consummation of the business combination. For illustrative purposes, as of May 25, 2017 (after giving effect to the redemptions of public shares redeemed in connection with the proposals approved by our shareholders on May 23, 2017), this would have amounted to approximately $10.05 per public share. If a public shareholder exercises its redemption rights, then it will be electing to exchange its GPIA ordinary shares (that become RMNI shares upon the domestication) for cash and will no longer own RMNI public shares. The redemption takes place following the domestication and accordingly it is RMNI public shares that are redeemed immediately after consummation of the second merger. See “ Extraordinary General Meeting of GPIA Shareholders—Redemption Rights ” in the accompanying joint proxy statement/prospectus for a detailed description of the procedures to be followed if you wish to redeem your RMNI public shares for cash.

Under the merger agreement, the consummation of the first merger is conditioned upon, among other things, (i) there being a minimum of $50,000,000 of cash available to GPIA (including the cash in our trust account and any cash provided by the Sponsor pursuant to its equity commitment) and (ii) there being a minimum amount of immediately available cash in the trust account of not less than $5,000,001 after giving effect to the redemption of GPIA ordinary shares that holders of GPIA ordinary shares validly elected to redeem in connection with the business combination. Therefore, unless these conditions are waived by GPIA, Let’s Go and Rimini Street, the merger agreement could terminate and the proposed business combination may not be consummated. In addition, the amendment, modification or waiver of the merger agreement in any manner that could reasonably be expected to be materially adverse to Rimini Street or the agents and lenders under the Credit Facility requires the prior written consent of the Origination Agent. There can be no assurance that GPIA, Let’s Go and Rimini Street would waive any such provision of the merger agreement, or that the agents and lenders under the Credit Facility would provide any required consents to such amendments, modifications or waivers. Furthermore, as provided in our memorandum and articles of association, in no event will we redeem our public shares in an amount that would cause our net tangible assets to be less than $5,000,001.

GPIA may enter into equity financing or debt financing in connection with the proposed business combination with the Sponsor or its affiliates or any third parties. The purposes of any such financings may include increasing the likelihood of GPIA having a minimum of $50,000,000 of available cash upon consummation of the first merger, which is a condition to consummation of the first merger. The merger agreement provides that any equity financing

be contingent upon closing of the business combination and further provides that any proposed financing be subject to the mutual agreement of GPIA and Rimini Street. Any equity issuances to the Sponsor or its affiliates would increase the relative percentage ownership of the Sponsor and, accordingly, would increase the percentage ownership of the initial shareholders. Any additional equity issuances would result in dilution of the relative ownership interest of the non-redeeming public shareholders or the former equity holders of Rimini Street. As the amount of any such equity issuances is not currently known, GPIA cannot provide exact figures as to percentage ownership that may result therefrom.

As disclosed in connection with our initial public offering on a registration statement filed with the Securities and Exchange Commission on Form S-1 (Reg. No. 333-203500) that became effective on May 19, 2015, if our initial business combination (as defined in our memorandum and articles of association) is paid for using equity or debt securities, or not all of the funds released from the trust account are used for payment of the consideration in connection with our initial business combination or used for redemptions of our ordinary shares, we may apply the balance of the cash released to us from the trust account for general corporate purposes, including for maintenance or expansion of operations of post-transaction businesses, the payment of principal or interest due on indebtedness incurred in completing our initial business combination, to fund the purchase of other companies or for working capital. Accordingly, after consummation of the business combination and after payment to public shareholders who elected to redeem their RMNI public shares, the funds in the trust account will be released to RMNI (as successor to GPIA as a result of the domestication) and used by RMNI to pay expenses incurred in connection with the business combination with Rimini Street and a fee to the underwriters of our initial public offering, and certain other fees to GPIA’s and Rimini Street’s advisors. Any remaining balance in the trust account would thereafter be available for general corporate purposes, including, but not limited to, the prepayment of amounts owed under the Credit Facility and to provide working capital for operations.

All GPIA shareholders are cordially invited to attend the extraordinary general meeting in person. To ensure your representation at the extraordinary general meeting, however, you are urged to complete, sign, date and return the enclosed proxy card as soon as possible. If you are a shareholder of record holding GPIA ordinary shares, you also may cast your vote in person at the extraordinary general meeting. If your shares are held in an account at a brokerage firm or bank, you must instruct your broker or bank on how to vote your shares or, if you wish to attend the extraordinary general meeting and vote in person, obtain a proxy from your broker or bank. If you do not vote or do not instruct your broker or bank how to vote, it will have no effect on the proposals because such action would not count as a vote cast at the extraordinary general meeting.

Your vote is important regardless of the number of shares you own. Whether you plan to attend the extraordinary general meeting or not, please sign, date and return the enclosed proxy card as soon as possible in the envelope provided. If your shares are held in “street name” or are in a margin or similar account, you should contact your broker to ensure that votes related to the shares you beneficially own are properly counted.

Your attention is directed to the joint proxy statement/prospectus accompanying this notice (including the annexes thereto) for a more complete description of the proposed business combination and related transactions and each of the proposals. We encourage you to read the accompanying joint proxy statement/prospectus carefully. If you have any questions or need assistance voting your ordinary shares, please contact Morrow Sodali LLC, our proxy solicitor, by calling (800) 662-5200, or banks and brokers can call collect at (203) 658-9400, or by emailing GPIA.info@morrowsodali.com.

Thank you for your participation. We look forward to your continued support.

IF YOU RETURN YOUR PROXY CARD WITHOUT AN INDICATION OF HOW YOU WISH TO VOTE, YOUR SHARES WILL NOT BE VOTED IN FAVOR OF ANY OF THE PROPOSALS. TO EXERCISE YOUR REDEMPTION RIGHTS, YOU MUST (I) IF YOU HOLD ORDINARY SHARES THROUGH UNITS, ELECT TO SEPARATE YOUR UNITS INTO THE UNDERLYING PUBLIC SHARES AND PUBLIC WARRANTS PRIOR TO EXERCISING YOUR REDEMPTION RIGHTS WITH RESPECT TO THE PUBLIC SHARES, (II) SUBMIT A WRITTEN REQUEST TO CONTINENTAL STOCK TRANSFER & TRUST COMPANY, GPIA’S TRANSFER AGENT, THAT RMNI REDEEM ALL OR A PORTION OF YOUR RMNI PUBLIC SHARES FOR CASH, AND (III) DELIVER YOUR ORDINARY SHARES TO CONTINENTAL STOCK TRANSFER & TRUST COMPANY, GPIA’S TRANSFER AGENT, PHYSICALLY OR ELECTRONICALLY USING DEPOSITORY TRUST COMPANY’S DWAC (DEPOSIT WITHDRAWAL AT CUSTODIAN) SYSTEM, IN EACH CASE IN ACCORDANCE WITH THE PROCEDURES AND DEADLINES DESCRIBED IN THE ACCOMPANYING JOINT PROXY STATEMENT/PROSPECTUS. IF THE BUSINESS COMBINATION IS NOT CONSUMMATED, THEN THE PUBLIC SHARES WILL NOT BE REDEEMED FOR CASH. IF YOU HOLD THE SHARES IN STREET NAME, YOU WILL NEED TO INSTRUCT THE ACCOUNT EXECUTIVE AT YOUR BANK OR BROKER TO WITHDRAW THE SHARES FROM YOUR ACCOUNT IN ORDER TO EXERCISE YOUR REDEMPTION RIGHTS. SEE “ EXTRAORDINARY GENERAL MEETING OF GPIA SHAREHOLDERS—REDEMPTION RIGHTS ” IN THE ACCOMPANYING PROXY STATEMENT/PROSPECTUS FOR MORE SPECIFIC INSTRUCTIONS.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of the transactions described in the accompanying joint proxy statement/prospectus, passed upon the merits or fairness of the merger agreement or the transactions contemplated thereby, or passed upon the adequacy or accuracy of the accompanying joint proxy statement/prospectus. Any representation to the contrary is a criminal offense.

RIMINI STREET, INC.

A Nevada Corporation
3993 Howard Hughes Parkway, Suite 500
Las Vegas, NV 89169

NOTICE OF SPECIAL MEETING OF STOCKHOLDERS
TO BE HELD ON [ • ], 2017

TO THE STOCKHOLDERS OF RIMINI STREET, INC.:

NOTICE IS HEREBY GIVEN that a special meeting of the stockholders (the “special meeting”) of Rimini Street, Inc., a Nevada corporation (“Rimini Street”), will be held at [•] Pacific Time, on [•], 2017, at [•]. You are cordially invited to attend the special meeting, which will be held for the following purposes:

These items of business are described in the accompanying joint proxy statement/prospectus, which we encourage you to read in its entirety before voting.

Only holders of record of Rimini Street capital stock at the close of business on [•], 2017 are entitled to notice of and to vote and have their votes counted at the special meeting and any adjournment of the special meeting.

We are providing the accompanying joint proxy statement/prospectus and accompanying proxy card to our stockholders in connection with the solicitation of proxies to be voted at the special meeting and at any adjournment of the special meeting. Whether or not you plan to attend the special meeting, we urge you to read the accompanying joint proxy statement/prospectus (and any documents incorporated into the accompanying joint proxy statement/prospectus by reference) carefully. Please pay particular attention to the section entitled “ Risk Factors ”.

After careful consideration, Rimini Street’s board of directors has determined that the Rimini Street business combination proposal and the Rimini Street preferred stock conversion proposal are in the best interests of Rimini Street and its stockholders and recommends that you vote or give instruction to vote “FOR” each of those proposals.

The existence of financial and personal interests of one or more of Rimini Street’s directors may result in a conflict of interest on the part of such director(s) between what he, she or they may believe is in the best interests of Rimini Street and its stockholders and what he, she or they may believe is best for himself, herself or themselves in determining to recommend that stockholders vote for the proposals. See the section entitled “ Rimini Street Business Combination Proposal—Interests of Rimini Street’s Directors and Officers in the Business Combination ” in the accompanying joint proxy statement/prospectus for a further discussion of this.

In connection with the mergers, Rimini Street stockholders representing a sufficient number of shares of Rimini Street capital stock necessary to approve the Rimini Street business combination proposal and the Rimini Street preferred stock conversion proposal have entered into a transaction support and voting agreement pursuant to which they have agreed to support and vote all of their shares in favor of such proposals.

Your vote is important. Whether or not you plan to attend the special meeting, please act promptly to vote your shares on the proposals described above. You may submit a proxy for your shares by completing, signing and dating the enclosed proxy card and returning it as promptly as possible in the enclosed postage-prepaid envelope.

You may revoke your proxy in the manner described in the accompanying joint proxy statement/prospectus at any time before it has been voted at the special meeting. If you attend the special stockholders meeting, you may vote your shares in person even if you have previously submitted a proxy.

You are entitled to appraisal rights in connection with the merger in accordance with Nevada law. See the discussion under “ Appraisal Rights ” of the accompanying joint proxy statement/ prospectus for more information.

Thank you for your participation. We look forward to your continued support.

JOINT PROXY STATEMENT FOR
EXTRAORDINARY GENERAL MEETING OF THE SHAREHOLDERS OF
GP INVESTMENTS ACQUISITION CORP.
(A CAYMAN ISLANDS EXEMPTED CORPORATION)
AND
SPECIAL MEETING OF THE STOCKHOLDERS OF
RIMINI STREET, INC. (A NEVADA CORPORATION)

PROSPECTUS FOR
571,645 UNITS (EACH UNIT COMPRISING ONE SHARE OF COMMON STOCK AND
ONE-HALF OF A WARRANT), 65,881,113 SHARES OF COMMON STOCK AND 8,625,000 WARRANTS TO ACQUIRE SHARES OF COMMON STOCK OF
GP INVESTMENTS ACQUISITION CORP. (AFTER ITS DOMESTICATION AS A CORPORATION INCORPORATED IN THE STATE OF DELAWARE),
THE CONTINUING ENTITY FOLLOWING THE DOMESTICATION (WHICH WILL BE RENAMED RIMINI STREET, INC. IMMEDIATELY AFTER CONSUMMATION OF THE SECOND MERGER)

The board of directors of GP Investments Acquisition Corp., a Cayman Islands exempted corporation (“GPIA”) and the board of directors of Rimini Street, Inc., a Nevada corporation (“Rimini Street”) have unanimously approved the business combination (the “business combination”) in accordance with the terms and subject to the conditions of an agreement and plan of merger, dated as of May 16, 2017 (as amended, the “merger agreement”), as amended by Amendment No. 1 thereto, dated June 30, 2017 (the “merger agreement amendment”), in each case, by and among GPIA, Let’s Go, Rimini Street and, solely in his capacity as the initial Holder Representative (as defined in the merger agreement) for the limited purposes set forth therein, the person specified as such in the merger agreement (the “Holder Representative”). Pursuant to the merger agreement, and following the domestication of GPIA to Delaware, Let’s Go Acquisition Corp., GPIA’s wholly-owned subsidiary (“Let’s Go”), will merge with and into Rimini Street, with Rimini Street as the surviving corporation (the “first merger”). The surviving corporation from the first merger will then merge with and into GP Investments Acquisition Corp. (after its domestication as a corporation incorporated in the State of Delaware), with GP Investments Acquisition Corp. being the surviving corporation (the “second merger”) and renamed “Rimini Street, Inc.” immediately after consummation of the second merger. Therefore, the business combination will be an integrated transaction resulting in Rimini Street merging with and into Rimini Street, Inc. (a corporation incorporated in the State of Delaware, as renamed immediately after consummation of the second merger).

Upon the domestication, GPIA will become GP Investments Acquisition Corp., a corporation incorporated in the State of Delaware), which corporation will be renamed Rimini Street, Inc. immediately after consummation of the second merger. As a change of entity name does not involve a change in the legal form of the entity, in this joint proxy statement/prospectus, “RMNI” refers to GP Investments Acquisition Corp. (after its domestication as a corporation incorporated in the State of Delaware), the continuing entity following the domestication, including subsequent to its change of name to Rimini Street, Inc., which shall occur immediately after consummation of the second merger.

As described in this joint proxy statement/prospectus, (i) GPIA’s shareholders are being asked to consider and vote upon (among other things) the proposed business combination with Rimini Street, a privately held operating company, and (ii) Rimini Street’s stockholders are being asked to consider and vote upon the proposed business combination with GPIA, a special purpose acquisition company and Rimini Street’s preferred stockholders are being asked to consider and vote upon the proposed preferred stock conversion referred to in this joint proxy statement/prospectus.

As a condition to closing the first merger, the board of directors of GPIA has unanimously approved a change of GPIA’s jurisdiction of incorporation by deregistering as an exempted company in the Cayman Islands and continuing and domesticating as a corporation incorporated under the laws of the State of Delaware (the “domestication”). To effect the domestication, GPIA will file a notice of deregistration with the Cayman Islands Registrar of Companies, together with the necessary accompanying documents, and file a certificate of incorporation and a certificate of corporate domestication with the Secretary of State of the State of Delaware, under which GPIA will be domesticated and continue as a Delaware corporation. On the effective date of the domestication, each currently issued and outstanding ordinary share, par value $0.0001 per share, of GPIA (the “GPIA ordinary shares”) will convert automatically by operation of law, on a one-for-one basis, into shares of common stock, par value $0.0001 per share, of GP Investments Acquisition Corp. (after its domestication as a corporation incorporated in the State of Delaware), which will be renamed “Rimini Street, Inc.” immediately after consummation of the second

merger (“RMNI common stock”). Similarly, outstanding warrants of GPIA will become warrants to acquire the corresponding shares of RMNI common stock and no other changes will be made to the terms of any outstanding warrants as a result of the domestication. In addition, outstanding units of GPIA will become units of RMNI and no other changes will be made to the terms of any outstanding units as a result of the domestication.

It is currently expected that the business combination will be consummated by August 31, 2017.

In accordance with the terms and subject to the conditions of the merger agreement, upon the effectiveness of the first merger, each share of then-issued and outstanding Rimini Street common stock (other than (i) shares of common stock and preferred stock (on an as-converted basis), if any, held as treasury stock, which will be cancelled upon the effectiveness of the first merger, and (ii) shares of Rimini Street common stock that are held by stockholders who have perfected and not withdrawn a demand for appraisal rights under applicable Nevada law) will automatically be cancelled and converted into and become the right to receive the applicable portion of the merger consideration. In accordance with the terms and subject to the conditions of the merger agreement and subject to certain adjustments set forth therein, the aggregate purchase price for the first merger and related transactions is $775 million, which amount will be (i) reduced by, among other things set forth in the merger agreement, the amount of the indebtedness of Rimini Street existing on the Closing Date (as defined in the merger agreement) of the first merger (including all make-whole obligations and exit or similar fees payable to any third party), (ii) increased by, among other things set forth in the merger agreement, the cash and cash equivalents held by or on behalf of Rimini Street on the Closing Date (as defined in the merger agreement) of the first merger, and (iii) reduced by the unpaid transaction fees and expenses associated with the first merger incurred by Rimini Street and its subsidiaries (as adjusted in accordance with the terms of the merger agreement, the “merger consideration”). The merger consideration is payable entirely in newly issued common stock of RMNI based on a per share issue price of $10.00 per share. The precise amount of such adjustments is to be calculated as of the Closing Date and is therefore not currently known. However, based on an illustrative Closing Date of May 31, 2017 (being the most recent date for which Rimini Street month end balance sheet data is available prior to the date of this joint proxy statement/prospectus), GPIA estimates a downward adjustment of approximately $156.5 million. This estimated adjustment is based on an illustrative Closing Date of May 31, 2017 (being the most recent date for which Rimini Street month end balance sheet data is available prior to the date of this joint proxy statement/prospectus) and such downward adjustment represents the net result of (i) a $175.3 million reduction in respect of the amount of the indebtedness of Rimini Street existing on the Closing Date (as defined in the merger agreement) of the first merger (including all make-whole obligations and exit or similar fees payable to any third party), (ii) a $32.4 million increase in respect of the cash and cash equivalents held by or on behalf of Rimini Street on the Closing Date (as defined in the merger agreement) of the first merger, and (iii) a $13.6 million reduction in respect of unpaid transaction fees and expenses associated with the first merger incurred by Rimini Street and its subsidiaries. Based on such estimated adjustment, upon consummation of the first merger the stockholders of Rimini Street immediately prior to consummation of the first merger will receive an aggregate number of shares of RMNI common stock equating to approximately $618.5 million (based on a per share issue price of $10.00 per share). The merger consideration is subject to adjustment to appropriately reflect the effect of any stock split, reverse stock split, stock dividend, reorganization, recapitalization, reclassification, combination, exchange of shares or other like change prior to consummation of the first merger, although no such events are currently contemplated.

It is currently expected that the business combination will be consummated by August 31, 2017. The estimation of the merger consideration described above is based on Rimini Street financial data as of May 31, 2017 and will change based upon, among other things, (i) the total debt obligations of Rimini Street on the Closing Date, which fluctuate in the ordinary course of business (including as a result of scheduled payments in respect of the Credit Facility between May 31, 2017 and August 31, 2017) and (ii) the cash and cash equivalents of Rimini Street on the Closing Date, which fluctuate in the ordinary course of business, including as a result of debt amortization payments.

Pursuant to the terms of the merger agreement and the related escrow agreement, 5,500,000 shares of RMNI common stock issued as merger consideration are subject to an indemnification escrow for any indemnification claims by the holders of ordinary shares of GPIA immediately prior to the effectiveness of the first merger.

Accordingly, the registration statement of which this joint proxy statement/prospectus forms part registers (i) 571,645 units of RMNI (each unit representing one share of common stock and one-half of one warrant) to be issued in the domestication (being the number of outstanding units on the date of this joint proxy/registration statement), (ii) 15,697,276 shares of common stock of RMNI to be issued in the domestication (being the number of outstanding public shares on the date of this joint proxy/registration statement), (iii) 8,625,000 warrants to acquire

shares of common stock of RMNI to be issued in the domestication (being the number of outstanding units on the date of this joint proxy/registration statement), and (iv) 50,183,837 shares of common stock of RMNI, being the number of shares of common stock of RMNI that could be issued to the stockholders of Rimini Street in respect of the merger consideration payable to them pursuant to the merger agreement. As the exact amount of the consideration is subject to adjustment at the closing of the proposed business combination, the number of shares referred to in clause (iv) in the preceding sentence represents GPIA’s good faith estimate of the estimated number of shares of RMNI to be paid to such stockholders as merger consideration, based on a per share issue price of $10.00 per share.

As of the date of this joint proxy statement/prospectus, there are 20,009,776 GPIA ordinary shares outstanding, of which GPIA’s Sponsor, GPIC, Ltd., a Bermuda company (the “Sponsor”), an affiliate of GP Investments, Ltd., owns 4,252,500 ordinary shares, and our independent directors own an aggregate of 60,000 ordinary shares. In addition, the Sponsor owns 6,062,500 warrants (the “private placement warrants”) that were issued in a private placement that closed simultaneously with the closing of GPIA’s initial public offering on May 26, 2015 (“initial public offering”) and an affiliate of the Sponsor owns 52,100 warrants that were acquired by such affiliate in the secondary market following GPIA’s initial public offering. As of the date of this joint proxy statement/prospectus, there is outstanding an aggregate of 14,687,500 warrants to acquire GPIA ordinary shares, which comprise the 6,062,500 private placement warrants held by the Sponsor and the 8,625,000 public warrants, of which 52,100 are held by an affiliate of the Sponsor. Each of the 17,250,000 units issued in GPIA’s initial public offering contains one-half of a warrant. As of the date of this joint proxy statement/prospectus, there were 571,645 units outstanding. Each warrant entitles the holder thereof to purchase one GPIA ordinary share and, following the domestication, will entitle the holder thereof to purchase one RMNI common share.

Assuming consummation of the business combination as of May 31, 2017 (being the most recent date for which Rimini Street month end balance sheet data is available prior to the date of this joint proxy statement/prospectus), immediately following the consummation of the business combination (without taking into account any GPIA ordinary shares held by Rimini Street stockholders prior to the consummation of the business combination, and assuming (i) that RMNI issues 50,183,837 shares of RMNI common stock to the former equityholders of Rimini Street pursuant to the merger agreement and that, at consummation of the business combination, there will be outstanding RMNI options and warrants held by former holders of Rimini Street options and warrants, pursuant to which up to 15,637,834 shares of RMNI common stock will be issuable in accordance with the terms of such RMNI options and warrants, (ii) that the Sponsor does not subscribe for any common shares pursuant to its equity commitment at or prior to the consummation of the business combination and (iii) that no public shareholders exercise their redemption rights), the former equityholders of Rimini Street are expected to own approximately 71.5% of RMNI’s common stock (or 65.5% of RMNI’s common stock on a fully-diluted basis) and GPIA’s current shareholders are expected to own approximately 28.5% of RMNI’s common stock (or 34.5% of RMNI’s common stock on a fully-diluted basis), which comprises (i) 6.2% of RMNI’s common stock (or 10.4% of RMNI’s common stock on a fully-diluted basis) expected to be owned by GPIA’s initial shareholders and (ii) 22.4% of RMNI’s common stock (or 24.2% of RMNI’s common stock on a fully-diluted basis) expected to be owned by GPIA’s public shareholders.

Assuming consummation of the business combination as of May 31, 2017 (being the most recent date for which Rimini Street month end balance sheet data is available prior to the date of this joint proxy statement/prospectus), immediately following the consummation of the business combination (without taking into account any GPIA ordinary shares held by Rimini Street stockholders prior to the consummation of the business combination, and assuming (i) that RMNI issues 50,183,837 shares of RMNI common stock to the former equityholders of Rimini Street pursuant to the merger agreement and that, at consummation of the business combination, there will be outstanding RMNI options and warrants held by former holders of Rimini Street options and warrants, pursuant to which up to 15,637,834 shares of RMNI common stock will be issuable in accordance with the terms of such RMNI options and warrants, (ii) that the Sponsor subscribes for 3,500,000 GPIA ordinary shares pursuant to its equity commitment at or prior to the consummation of the business combination and (iii) that holders of 14,205,056 GPIA ordinary shares (or 90.5% of the outstanding public shares) (being our estimate of the maximum number of GPIA public shares that could be redeemed in order for GPIA to have $50,000,000 of available cash upon consummation of the first merger, after taking into account the Sponsor’s maximum equity commitment of $35,000,000) elect to redeem their ordinary shares in connection with the business combination), the former equityholders of Rimini Street are expected to own approximately 84.4% of RMNI’s common stock (or 73.3% of RMNI’s common stock on a fully-diluted basis) and GPIA’s current shareholders are expected to own approximately 15.6% of RMNI’s common

stock (or 26.7% of RMNI’s common stock on a fully-diluted basis), which comprises (i) 13.1% of RMNI’s common stock (or 15.5% of RMNI’s common stock on a fully-diluted basis) expected to be owned by GPIA’s initial shareholders and (ii) 2.5% of RMNI’s common stock (or 11.3% of RMNI’s common stock on a fully-diluted basis) expected to be owned by GPIA’s public shareholders.

GPIA may enter into equity financing or debt financing in connection with the proposed business combination from the Sponsor or its affiliates or any third parties. The purposes of any such financings may include increasing the likelihood of GPIA having a minimum of $50,000,000 of available cash upon consummation of the first merger, which is a condition to consummation of the first merger. The merger agreement provides that any equity financing be contingent upon closing of the business combination and further provides that any proposed financing be subject to the mutual agreement of GPIA and Rimini Street. Any equity issuances to the Sponsor or its affiliates would increase the relative percentage ownership of the Sponsor and, accordingly, would increase the percentage ownership of the initial shareholders. Any additional equity issuances would result in dilution of the relative ownership interest of the non-redeeming public shareholders or the former equity holders of Rimini Street. As the amount of any such equity issuances is not currently known, GPIA cannot provide exact figures as to percentage ownership that may result therefrom.

GPIA has entered into a lock-up letter, dated May 16, 2017 (the “lock-up letter”), with Seth A. Ravin (as trustee of a trust holding common and preferred stock of Rimini Street), Thomas C. Shay and Adams Street Partners LLC and certain Adams Street fund limited partnerships (together, the “Lock-up Stockholders”). Pursuant to the lock-up letter, among other things, the Lock-up Stockholders have agreed not to transfer or otherwise dispose of any shares of RMNI common stock that they receive upon consummation of the business combination for a period of twelve months from the effectiveness of the first merger (the “lock-up period”), subject to certain exceptions, including, among other things, if the last sale price equals or exceeds $12.00 per share (as adjusted for share splits, share dividends, reorganizations, recapitalizations and the like) for any 20 trading days within any 30-trading day period commencing at least 150 days after the effectiveness of the first merger. Immediately following the consummation of the business combination (without taking into account any GPIA ordinary shares held by Rimini Street stockholders prior to the consummation of the business combination, and assuming (i) that the Sponsor does not subscribe for any common shares pursuant to its equity commitment at or prior to the consummation of the business combination, (ii) that RMNI issues 50,183,837 shares of RMNI common stock to the former equityholders of Rimini Street pursuant to the merger agreement and (iii) that no public shareholders exercise their redemption rights), the Lock-up Stockholders are expected to hold in aggregate approximately 59.8% of the outstanding RMNI common stock (or 42.5% of RMNI’s common stock on a fully-diluted basis).

Proposals to approve the merger agreement and the Rimini Street preferred stock conversion discussed in this joint proxy statement/prospectus will be presented at the a special meeting of the stockholders of Rimini Street (the “special meeting”) scheduled to be held on [•], 2017.

Proposals to approve the merger agreement and the other matters discussed in this joint proxy statement/prospectus will be presented at the extraordinary general meeting of the shareholders of GPIA (the “extraordinary general meeting”) scheduled to be held on [•], 2017.

GPIA’s units, ordinary shares and warrants are currently listed on the NASDAQ Capital Market (“NASDAQ”) under the symbols “GPIAU”, “GPIA” and “GPIAW”, respectively. GPIA has applied for listing, to be effective at the time of the business combination, of its units, common stock and warrants on NASDAQ under the proposed symbols “RMNIU”, “RMNI” and “RMNIW”, respectively. It is a condition of the consummation of the first merger that GPIA receive confirmation from NASDAQ that the combined company has been conditionally approved for listing on NASDAQ, but there can be no assurance such listing conditions will be met or that GPIA will obtain such confirmation from NASDAQ. If such listing conditions are not met or if such confirmation is not obtained, the first merger will not be consummated unless the NASDAQ condition set forth in the merger agreement is waived by the parties.

In order to consummate the business combination, Rimini Street was required to obtain the consent of a majority of the lenders under the Credit Facility as described below. Certain waiver letters, dated as of May 16, 2017, agreed to by Rimini Street and the agents and lenders provide for consent by the agents and lenders to consummate the business combination. The waiver letters also provide for the waiver of certain events of default under the Credit Facility that may arise as a result of the consummation of the business combination. As a condition to effectiveness of the waiver letters, Rimini Street is required to make a minimum payment to the lenders of $35.0 million to reduce

certain outstanding obligations under the Credit Facility. The amendment, modification or waiver of the merger agreement in any manner that could reasonably be expected to be materially adverse to Rimini Street or the agents and lenders under the Credit Facility requires the prior written consent of the Origination Agent. There can be no assurance that GPIA, Let’s Go and Rimini Street would waive any such provision of the merger agreement, or that the agents and lenders under the Credit Facility would provide any required consents to such amendments, modifications or waivers.

Prior to consummation of the business combination, Rimini Street and GPIA may jointly elect to offer the lenders under the Credit Facility the ability to convert up to $21.0 million of obligations under the Credit Facility at $10.00 per share for 2,100,000 GPIA ordinary shares, effective immediately prior to the first merger. If Rimini Street and GPIA elect to make this offer, the lenders under the Credit Facility are under no obligation to accept it.

In this joint proxy statement/prospectus, (i) the term “ordinary shares” is used to refer to the ordinary share capital of GPIA, (ii) the term “public shares” is used to refer to the ordinary shares that were offered and sold by GPIA in its initial public offering that was registered pursuant to the Registration Statement on Form S-1 (333-203500), (iii) the term “public shareholders” refers to holders of public shares, whether acquired in GPIA’s initial public offering or acquired in the secondary market, (iv) the term “public warrants” refers to the warrants to acquire GPIA ordinary shares that were offered and sold by GPIA in its initial public offering that was registered pursuant to the Registration Statement on Form S-1 (333-203500), (v) the term “initial shareholders” means the Sponsor and GPIA’s independent directors at the time of its initial public offering, (vi) the term “founder shares” refers to the ordinary shares that are held by the Sponsor and GPIA’s independent directors, which comprise 4,312,500 ordinary shares, or 21.6% of the GPIA ordinary shares outstanding as of the date of this joint proxy statement/prospectus and (vii) unless otherwise indicated, references to “we”, “us” and “our” are intended to refer to GPIA, except that in the sections related to Rimini Street, references to “we”, “us” and “our” are intended to refer to Rimini Street.

This joint proxy statement/prospectus provides shareholders of GPIA with detailed information about the business combination and other matters to be considered at the extraordinary general meeting of GPIA’s shareholders. This joint proxy statement/prospectus provides stockholders of Rimini Street with detailed information about the business combination and other matters to be considered at the special meeting of Rimini Street’s stockholders. We encourage you to carefully read this entire document and the documents incorporated in this joint proxy statement/prospectus by reference. You should also carefully consider the risk factors described in “ Risk Factors ” beginning on page 62 of this joint proxy statement/prospectus.

These securities have not been approved or disapproved by the Securities and Exchange Commission (the “SEC”) or any state securities commission nor has the Securities and Exchange Commission or any state securities commission passed upon the accuracy or adequacy of this joint proxy statement/prospectus. Any representation to the contrary is a criminal offense.

This joint proxy statement/prospectus is dated [•], 2017, and is first being mailed to
GPIA’s shareholders and Rimini Street’s stockholders on or about [•], 2017.

The forward-looking statements contained in this joint proxy statement/prospectus and in any document incorporated by reference in this joint proxy statement/prospectus are based on current expectations and beliefs concerning future developments and their potential effects on us and/or Rimini Street. There can be no assurance that future developments affecting us and/or Rimini Street will be those that we and/or Rimini Street have anticipated. These forward-looking statements involve a number of risks, uncertainties (some of which are beyond our control or the control of Rimini Street) or other assumptions that may cause actual results or performance to be materially different from those expressed or implied by these forward-looking statements. These risks and uncertainties include, but are not limited to, those factors described under the heading “ Risk Factors ” beginning on page 62 of this joint proxy statement/prospectus. Should one or more of these risks or uncertainties materialize, or should any of our assumptions prove incorrect, actual results may vary in material respects from those projected in these forward-looking statements. We and/or Rimini Street undertake no obligation to update or revise any forward-looking statements, whether as a result of new information, future events or otherwise, except as may be required under applicable securities laws.

Before (i) a GPIA shareholder grants its proxy or instructs how its vote should be cast or vote on the proposals to be put to the extraordinary general meeting, or (ii) a Rimini Street stockholder grants its proxy or instructs how its vote should be cast or vote on the proposals to be put to the special meeting, it should be aware that the occurrence of the events described in the “Risk Factors” section and elsewhere in this joint proxy statement/prospectus may adversely affect Rimini Street, GPIA, or, following the consummation of the business combination, RMNI.

QUESTIONS AND ANSWERS FOR ALL SHAREHOLDERS

Consummation of the business combination requires the approval of (i) GPIA shareholders holding a majority of the outstanding ordinary shares voting at an extraordinary general meeting of shareholders that is being called by GPIA and (ii) the holders of (a) the majority of the voting power of shares of Rimini Street capital stock, (b) more than 50% of the outstanding shares of Rimini Street Series B Preferred Stock and Series C Preferred Stock, voting as a single class on an as-converted basis (each holder of Rimini Street Preferred Stock shall be entitled to the number of votes equal to the number of shares of Rimini Street Class B Common Stock or Rimini Street Class A Common Stock, as applicable, into which the shares of Rimini Street Preferred Stock held by such holder could be converted as of the record date), and (c) the majority of the outstanding shares of Rimini Street Class A Common Stock and Rimini Street Class B Common Stock, voting as a single class, voting at a special meeting of stockholders that is being called by Rimini Street.

On the effective date of the domestication, each currently issued and outstanding ordinary share, par value $0.0001 per share, of GPIA will automatically convert by operation of law, on a one-for-one basis, into shares of common stock, par value $0.0001 per share, of GP Investments Acquisition Corp. (after its domestication as a corporation incorporated in the State of Delaware), which will be renamed “Rimini Street, Inc.” immediately after consummation of the second merger.

THE VOTE OF SHAREHOLDERS IS IMPORTANT. SHAREHOLDERS ARE ENCOURAGED TO VOTE AS SOON AS POSSIBLE AFTER CAREFULLY REVIEWING THIS JOINT PROXY STATEMENT/PROSPECTUS.

as treasury stock, which will be cancelled upon the effectiveness of the business combination) will be cancelled and converted into and become the right to receive the applicable portion of the merger consideration. Further, whether vested or unvested, each vested or unvested option to purchase shares of the common stock of Rimini Street under an incentive plan automatically will be cancelled and converted into the right to receive the applicable portion of the merger consideration as more particularly set forth in the merger agreement.

In accordance with the terms and subject to the conditions of the merger agreement and subject to certain adjustments set forth therein, the aggregate purchase price for the first merger and related transactions is $775 million, which amount will be (i) reduced by, among other things set forth in the merger agreement, the amount of the indebtedness of Rimini Street existing on the Closing Date (as defined in the merger agreement) of the first merger (including all make-whole obligations and exit or similar fees payable to any third party), (ii) increased by, among other things set forth in the merger agreement, the cash and cash equivalents held by or on behalf of Rimini Street on the Closing Date (as defined in the merger agreement) of the first merger, and (iii) decreased by the unpaid transaction fees and expenses associated with the business combination incurred by Rimini Street and its subsidiaries. The merger consideration is payable entirely in newly issued common stock of RMNI based on a per share issue price of $10.00 per share.

The precise amount of such adjustments is to be calculated as of the Closing Date and is therefore not currently known. However, based on an illustrative Closing Date of May 31, 2017 (being the most recent date for which Rimini Street month end balance sheet data is available prior to the date of this joint proxy statement/prospectus), GPIA estimates a downward adjustment of approximately $156.5 million. This estimated adjustment is based on an illustrative Closing Date of May 31, 2017 (being the most recent date for which Rimini Street month end balance sheet data is available prior to the date of this joint proxy statement/prospectus) and such downward adjustment represents the net result of (i) a $175.3 million reduction in respect of the amount of the indebtedness of Rimini Street existing on the Closing Date (as defined in the merger agreement) of the first merger (including all make-whole obligations and exit or similar fees payable to any third party), (ii) a $32.4 million increase in respect of the cash and cash equivalents held by or on behalf of Rimini Street on the Closing Date (as defined in the merger agreement) of the first merger, and (iii) a $13.6 million reduction in respect of unpaid transaction fees and expenses associated with the first merger incurred by Rimini Street and its subsidiaries. Based on such estimated adjustment, upon consummation of the business combination the stockholders of Rimini Street immediately prior to consummation of the first merger will receive an aggregate number of shares of RMNI common stock equating to approximately $618.5 million (based on a per share issue price of $10.00 per share). The merger consideration is subject to adjustment to appropriately reflect the effect of any stock split, reverse stock split, stock dividend, reorganization, recapitalization, reclassification, combination, exchange of shares or other like change prior to consummation of the first merger, although no such events are currently contemplated.

It is currently expected that the business combination will be consummated by August 31, 2017. The estimation of the merger consideration described above is based on Rimini Street financial data as of May 31, 2017 and will change based upon, among other things, (i) the total debt obligations of Rimini Street on the Closing Date, which fluctuate in the ordinary course of business (including as a result of scheduled payments in respect of the Credit Facility between May 31, 2017 and August 31, 2017) and (ii) the cash and cash equivalents of Rimini Street on the Closing Date, which fluctuate in the ordinary course of business, including as a result of debt amortization payments.

warrants and (iii) that no public shareholders exercise their redemption rights), the former equityholders of Rimini Street are expected to own approximately 71.5% of the outstanding RMNI common stock and the current holders of GPIA ordinary shares are expected to own approximately 28.5% of the outstanding RMNI common stock.

Assuming consummation of the business combination as of May 31, 2017 (being the most recent date for which Rimini Street month end balance sheet data is available prior to the date of this joint proxy statement/prospectus), immediately following the consummation of the business combination (without taking into account any GPIA ordinary shares held by Rimini Street stockholders prior to the consummation of the business combination), and assuming (i) that the Sponsor subscribes for 3,500,000 GPIA ordinary shares pursuant to its equity commitment at or prior to the consummation of the business combination, (ii) that RMNI issues 50,183,837 shares of RMNI common stock to the former equityholders of Rimini Street pursuant to the merger agreement and that, at consummation of the business combination, there will be outstanding RMNI options and warrants held by former holders of Rimini Street options and warrants, pursuant to which up to 15,637,834 shares of RMNI common stock will be issuable in accordance with the terms of such RMNI options and warrants and (iii) that holders of 14,205,056 GPIA ordinary shares (or 90.5% of the outstanding public shares) (being our estimate of the maximum number of GPIA public shares that could be redeemed in order for GPIA to have $50,000,000 of available cash upon consummation of the first merger, after taking into account the Sponsor’s maximum equity commitment of $35,000,000) elect to redeem their ordinary shares in connection with the business combination, the former equityholders of Rimini Street are expected to own approximately 84.4% of the outstanding RMNI common stock and the current holders of GPIA ordinary shares are expected to own approximately 15.6% of the outstanding RMNI common stock.

There are currently outstanding an aggregate of 14,687,500 warrants to acquire GPIA ordinary shares, which comprise the 6,062,500 private placement warrants held by the Sponsor and the 8,625,000 public warrants, of which 52,100 are held by an affiliate of the Sponsor. Each of the 17,250,000 units issued in our initial public offering contains one-half of a warrant. As of the date of this joint proxy statement/prospectus, there were 571,645 units outstanding. Each warrant entitles the holder thereof to purchase one GPIA ordinary share and, following the domestication, will entitle the holder thereof to purchase one RMNI common share. Therefore, as of the date of this joint proxy statement/prospectus, if we assume that each outstanding warrant is exercised and one ordinary share is issued as a result of such exercise, our fully-diluted share capital would be 34,697,276 ordinary shares.

Assuming consummation of the business combination as of May 31, 2017 (being the most recent date for which Rimini Street month end balance sheet data is available prior to the date of this joint proxy statement/prospectus), immediately following the consummation of the business combination (without taking into account any GPIA ordinary shares held by Rimini Street stockholders prior to the consummation of the business combination, assuming (i) that the Sponsor does not subscribe for any common shares pursuant to its equity commitment at or prior to the consummation of the business combination, (ii) that RMNI issues 50,183,837 shares of RMNI common stock to the former equityholders of Rimini Street pursuant to the merger agreement and that, at consummation of the business combination, there will be outstanding RMNI options and warrants held by former holders of Rimini Street options and warrants, pursuant to which up to 15,637,834 shares of RMNI common stock will be issuable in accordance with the terms of such RMNI options and warrants and (iii) that no public shareholders exercise their redemption rights), calculated on a fully-diluted basis, the former equityholders of Rimini Street are expected to own approximately 65.5% of the fully-diluted share capital of RMNI and the current holders of GPIA ordinary shares are expected to own approximately 34.5% of the fully-diluted share capital of RMNI.

Assuming consummation of the business combination as of May 31, 2017 (being the most recent date for which Rimini Street month end balance sheet data is available prior to the date of this joint proxy statement/prospectus), immediately following the consummation of the business combination (without taking into account any GPIA ordinary shares held by Rimini Street stockholders prior to the consummation of the business combination, assuming (i) that the Sponsor subscribes for 3,500,000 GPIA ordinary shares pursuant to its equity commitment at or prior to the consummation of the business combination, (ii) that RMNI issues 50,183,837 shares of RMNI common stock to the former equityholders of Rimini Street pursuant to the merger agreement and that, at consummation of the business combination, there will be outstanding RMNI options and warrants held by former holders of Rimini Street options and warrants, pursuant to which up to 15,637,834

shares of RMNI common stock will be issuable in accordance with the terms of such RMNI options and warrants and (iii) that holders of 14,205,056 GPIA ordinary shares (or 90.5% of the outstanding public shares) (being our estimate of the maximum number of GPIA public shares that could be redeemed in order for GPIA to have $50,000,000 of available cash upon consummation of the first merger, after taking into account the Sponsor’s maximum equity commitment of $35,000,000)), calculated on a fully-diluted basis, the former equityholders of Rimini Street are expected to own approximately 73.3% of the fully-diluted share capital of RMNI and the current holders of GPIA ordinary shares are expected to own approximately 26.7% of the fully-diluted share capital of RMNI.

To effect the domestication, GPIA will file a notice of deregistration with the Cayman Islands Registrar of Companies, together with the necessary accompanying documents, and file a certificate of incorporation and a certificate of corporate domestication with the Secretary of State of the State of Delaware, under which GPIA will be domesticated and continue as a Delaware corporation.

The approval of the domestication proposal is a condition to the closing of the merger agreement. The approval of the domestication proposal requires a special resolution under the Cayman Islands Companies Law, being the affirmative vote of the holders of at least two-thirds of the then outstanding GPIA ordinary shares who, being present and entitled to vote at the extraordinary general meeting, vote at the extraordinary general meeting. Abstentions and broker non-votes, while considered present for the purposes of establishing a quorum, will not count as votes cast at the extraordinary general meeting.

As disclosed in connection with our initial public offering on a registration statement filed with the Securities and Exchange Commission on Form S-1 (Reg. No. 333-203500) that became effective on May 19, 2015, if our initial business combination (as defined in the amended and restated memorandum and articles of association of GPIA (as amended by a special resolution of shareholders passed on May 23, 2017) (our “memorandum and articles of association”)) is paid for using equity or debt securities, or not all of the funds released from the trust account are used for payment of the consideration in connection with our initial business combination or used for redemptions of our ordinary shares, we may apply the balance of the cash released to us from the trust account for general corporate purposes, including for maintenance or expansion of operations of post-transaction businesses, the payment of principal or interest due on indebtedness incurred in completing our initial business combination, to fund the purchase of other companies or for working capital.

Accordingly, after consummation of the business combination and after payment to redeeming shareholders, the funds in the trust account will be released to RMNI (as successor to GPIA as a result of the domestication) and used by RMNI to pay expenses incurred by GPIA and Rimini Street in connection with the business combination. Such expenses include, among others (i) a fee to the underwriters of our initial public offering of $6,037,500, (ii) fees and expenses payable to our investment banking advisors for merger and acquisition advisory services of approximately $9.5 million and (iii) professional fees and expenses of our consultants, accountants and legal counsel of approximately $7.8 million. Any remaining balance in the trust account would thereafter be available for general corporate purposes, including, but not limited to, the prepayment of amounts owed under the Credit Facility (as described below) and to provide working capital for operations.

In order to consummate the business combination, Rimini Street was required to obtain the consent of a majority of the lenders under the Credit Facility. Certain waiver letters, dated as of May 16, 2017, agreed to by Rimini Street and the agents and lenders provide for consent by the agents and lenders to consummate the business combination. The waiver letters also provide for the waiver of certain events of default under the Credit Facility that may arise as a result of the consummation of the business combination. As a condition to effectiveness of the waiver letters, Rimini Street is required to make a minimum payment to the lenders of $35.0 million to reduce certain outstanding obligations under the Credit Facility.

Under the merger agreement, the consummation of the first merger is conditioned upon, among other things, (i) there being a minimum of $50,000,000 of cash available to GPIA (including the cash in our trust account and any cash provided by the Sponsor pursuant to its equity commitment) and (ii) there being a minimum amount of immediately available cash in the trust account of not less than $5,000,001 after giving effect to the redemption of GPIA ordinary shares that holders of GPIA ordinary shares validly elected to redeem in connection with the first merger. Therefore, unless these conditions are waived by GPIA, Let’s Go and Rimini Street, the merger agreement could terminate and the proposed first merger may not be consummated. In addition, the amendment, modification or waiver of the merger agreement in any manner that could reasonably be expected to be materially adverse to Rimini Street or the agents and lenders under the Credit Facility requires the prior written consent of the Origination Agent. There can be no assurance that GPIA, Let’s Go and Rimini Street would waive any such provision of the merger agreement, or that the agents and lenders under the Credit Facility would provide any required consents to such amendments, modifications or waivers. Furthermore, as provided in our memorandum and articles of association, in no event will we redeem our public shares in an amount that would cause our net tangible assets to be less than $5,000,001.

In addition, with fewer public shares and public shareholders, the trading market for RMNI’s common stock may be less liquid than the market for GPIA’s ordinary shares was prior to consummation of the business combination and RMNI may not be able to meet the listing standards for NASDAQ or another national securities exchange. In addition, with less funds available from the trust account, the working capital infusion from the trust account into Rimini Street’s business will be reduced.

The amendment, modification or waiver of the merger agreement in any manner that could reasonably be expected to be materially adverse to Rimini Street or the agents and lenders under the Credit Facility requires the prior written consent of the Origination Agent. There can be no assurance that GPIA, Let’s Go and Rimini Street would waive any such provision of the merger agreement, or that the agents and lenders under the Credit Facility would provide any required consents to such amendments, modifications or waivers.

For more information about conditions to the consummation of the first merger see “ GPIA Business Combination Proposal—The Merger Agreement—Conditions to Closing of the First Merger ”.

QUESTIONS AND ANSWERS FOR SHAREHOLDERS OF GPIA

In addition to the foregoing proposals, the shareholders also may be asked to consider and vote upon a proposal to adjourn the extraordinary general meeting to a later date or dates to permit further solicitation and vote of proxies if, based upon the tabulated vote at the time of the extraordinary general meeting, each of the condition precedent proposals have not been approved. See “ GPIA Adjournment Proposal ”.

GPIA will hold the extraordinary general meeting of its shareholders to consider and vote upon these proposals. This joint proxy statement/prospectus contains important information about the proposed business combination and the other matters to be acted upon at the extraordinary general meeting. Shareholders of GPIA should read it carefully.

After careful consideration, GPIA’s board of directors has determined that the business combination proposal, the domestication proposal, each of the organizational documents proposals, the stock issuance proposal and the adjournment proposal are in the best interests of GPIA and its shareholders and unanimously recommends that you vote or give instruction to vote “FOR” each of those proposals.

The existence of financial and personal interests of one or more of GPIA’s directors may result in a conflict of interest on the part of such director(s) between what he or they may believe is in the best interests of GPIA and its shareholders and what he or they may believe is best for himself or themselves in determining to recommend that shareholders vote for the proposals. See the section entitled “ GPIA Business Combination Proposal—Interests of GPIA’s Directors and Officers in the Business Combination ” for a further discussion of this.

THE VOTE OF SHAREHOLDERS IS IMPORTANT. SHAREHOLDERS ARE ENCOURAGED TO VOTE AS SOON AS POSSIBLE AFTER CAREFULLY REVIEWING THIS JOINT PROXY STATEMENT/PROSPECTUS.

These factors include, among others, Rimini Street is involved in ongoing litigation with Oracle, without near term visibility as to litigation outcome; Rimini Street has sizeable debt in place, not all of which will be repaid at consummation of the business combination; Rimini Street may face increased competition in the marketplace as its business grows in share and prominence, and as competitors are attracted to the market opportunity; Rimini Street may experience an increase in the cost of delivering its service based on the cost of hiring experienced software engineers; Rimini Street could face impediments to its continued growth if it is unable to

continue hiring effective salespeople to win new business, or if its existing salespeople experience lower productivity; Rimini Street faces a business threat of customer migration to enterprise software vendors, products and releases for which it does not provide software products or services, as customers may choose to abandon their existing enterprise software solutions in favor of such offerings; Rimini Street could face a business risk from an intellectual property perspective if customers’ software licenses do not permit Rimini Street to service the software; Rimini Street could be challenged to sufficiently service new software applications as the underlying technology continues to evolve; and Rimini Street could experience slower growth if customers upgrade or otherwise renew their maintenance agreements with their legacy software vendor.

These factors are discussed in greater detail in the section entitled “ GPIA Business Combination Proposal—GPIA’s Board of Director’s and the Special Transaction Committee’s Reasons for the Business Combination ”, as well as in the sections entitled “ Risk Factors—Risks Related to Rimini Street’s Business Operations and Industry ”.

Notwithstanding the foregoing, a holder of public shares, together with any affiliate of such public shareholder or any other person with whom such public shareholder is acting in concert or as a “group” (as defined in Section 13(d)(3) of the Securities Exchange Act of 1934, as amended (“Exchange Act”)), will be restricted from redeeming its RMNI public shares with respect to more than an aggregate of 20% of the public shares. Accordingly, if a public shareholder, alone or acting in concert or as a group, seeks to redeem more than 20% of the public shares, then any such shares in excess of that 20% limit would not be redeemed for cash.

Our initial shareholders entered into the insider letter agreement, pursuant to which they have agreed to waive their redemption rights with respect to their founder shares and public shares in connection with the completion of a business combination.

Under the merger agreement, the consummation of the merger is conditioned upon, among other things, (i) there being a minimum of $50,000,000 of cash available to GPIA (including the cash in our trust account and any cash provided by the Sponsor pursuant to its equity commitment) and (ii) there being a minimum amount of immediately available cash in the trust account of not less than $5,000,001 after giving effect to the redemption of GPIA ordinary shares that holders of GPIA ordinary shares validly elected to redeem in connection with the business combination. Therefore, unless these conditions are waived by GPIA, Let’s Go and Rimini Street, the merger agreement could terminate and the proposed business combination may not be consummated. The amendment, modification or waiver of the merger agreement in any manner that could reasonably be expected to be materially adverse to Rimini Street or the agents and lenders under the Credit Facility requires the prior written consent of the Origination Agent. There can be no assurance that GPIA, Let’s Go and Rimini Street would waive any such provision of the merger agreement, or that the agents and lenders under the Credit Facility would provide any required consents to such amendments, modifications or waivers. Furthermore, as provided

in our memorandum and articles of association, in no event will we redeem our public shares in an amount that would cause our net tangible assets to be less than $5,000,001 (so that we are not subject to the SEC’s “penny stock” rules).

Holders of GPIA public shares should complete the procedures for electing to redeem their GPIA public shares in the manner described above prior to 5:00 p.m. Eastern Time on [ • ], 2017 (two business days before the extraordinary general meeting).

The address of Continental Stock Transfer & Trust Company, GPIA’s transfer agent, is listed under the question “ Who can help answer my questions ?” below.

Holders of units must elect to separate the underlying public shares and public warrants prior to exercising redemption rights with respect to the public shares. If holders hold their units in an account at a brokerage firm or bank, holders must notify their broker or bank that they elect to separate the units into the underlying public shares and public warrants, or if a holder holds units registered in its own name, the holder must contact Continental Stock Transfer & Trust Company, GPIA’s transfer agent, directly and instruct them to do so.

Any holder of public shares will be entitled to request that their RMNI public shares be redeemed for a pro rata portion of the amount then on deposit in the trust account as of two business days prior to the consummation of the business combination including interest earned on the funds held in the trust account and not previously released to us. For illustrative purposes, as of May 25, 2017 (after giving effect to the redemptions of public shares redeemed in connection with the Extension (as defined below)), this would have amounted to approximately $10.05 per public share. However, the proceeds deposited in the trust account could become subject to the claims of our creditors, if any, which could have priority over the claims of our public shareholders, regardless of whether such public shareholders vote for or against the business combination proposal. Therefore, the per share distribution from the trust account in such a situation may be less than originally expected due to such claims. Your vote on any proposal other than the business combination proposal will have no impact on the amount you will receive upon exercise of your redemption rights. It is expected that the funds to be distributed to public shareholders electing to redeem their RMNI public shares will be distributed promptly after the consummation of the business combination.

If you are a holder of public shares, you may exercise your redemption rights by submitting your request in writing to Continental Stock Transfer & Trust Company, GPIA’s transfer agent, at the address listed at the end of this section.

Any request for redemption, once made by a holder of public shares, may be withdrawn at any time up to the time the vote is taken with respect to the business combination proposal at the extraordinary general meeting. If you deliver your shares for redemption to Continental Stock Transfer & Trust Company, GPIA’s transfer agent, and later decide prior to the extraordinary general meeting not to elect redemption, you may request that GPIA instruct its transfer agent to return the shares (physically or electronically). You may make such request by contacting Continental Stock Transfer & Trust Company, GPIA’s transfer agent, at the phone number or address listed at the end of this section.

Any corrected or changed written exercise of redemption rights must be received by Continental Stock Transfer & Trust Company, GPIA’s transfer agent, prior to the vote taken on the business combination proposal at the extraordinary general meeting. No request for redemption will be honored unless the holder’s stock has been delivered (either physically or electronically) to Continental Stock Transfer & Trust Company, GPIA’s transfer agent, at least two business days prior to the vote at the extraordinary general meeting.

If a holder of public shares properly makes a request for redemption and the public shares are delivered as described above, then, if the business combination is consummated, RMNI will redeem RMNI public shares for a pro rata portion of funds deposited in the trust account, calculated as of two business days prior to the consummation of the business combination.

If you are a holder of public shares and you exercise your redemption rights, it will not result in the loss of any GPIA warrants that you may hold.

Additionally, because the domestication will occur immediately prior to the redemption of any RMNI shareholder, U.S. Holders exercising redemption rights will be subject to the potential tax consequences of Section 367 of the U.S. Internal Revenue Code of 1986, as amended (the “Code”) as well as potential tax consequences of the U.S. federal income tax rules relating to “passive foreign investment companies” (“PFIC”). The tax consequences of Section 367 of the Code and the PFIC rules are discussed more fully below under “ U.S. Federal Income Tax Considerations ” beginning on page 163 of this joint proxy statement/prospectus.

All holders of public shares considering exercising their redemption rights are strongly urged to consult their tax advisor for a full description and understanding of the tax consequences of an exercise of redemption rights, including the applicability and effect of U.S. federal, state, local and foreign income and other tax laws.

As discussed further under “ U.S. Federal Income Tax Considerations ” below, GPIA believes that it is likely treated as a “passive foreign investment company”, or PFIC, for U.S. federal income tax purposes. In such case, notwithstanding the foregoing U.S. federal income tax consequences of the domestication, proposed Treasury Regulations under Section 1291(f) of the Code (which have a retroactive effective date), if finalized in their current form, generally would require a U.S. Holder to recognize gain on the exchange of GPIA ordinary shares or warrants for RMNI common stock or warrants pursuant to the domestication. The tax on any such gain would be imposed at the rate applicable to ordinary income and an interest charge would apply based on a complex set of rules. However, it is difficult to predict whether, in what form, and with what effective date, final Treasury Regulations under Section 1291(f) of the Code will be adopted. Importantly, however, U.S. Holders that make or have made certain elections discussed further under “ U.S. Federal Income Tax Considerations—Impact of PFIC Rules on Certain U.S. Holders ” with respect to their GPIA ordinary shares are generally not subject to the same gain recognition rules under the currently proposed Treasury Regulations under Section 1291(f) of the Code. For a more complete discussion of the potential application of the PFIC rules to U.S. Holders as a result of the domestication, see “ U.S. Federal Income Tax Considerations ” beginning on page 163 of this joint proxy statement/prospectus.

Additionally, the domestication may cause non-U.S. Holders (as defined in “ U.S. Federal Income Tax Considerations ” below) to become subject to U.S. federal income withholding taxes on any dividends paid in respect of such non-U.S. Holder’s RMNI common stock subsequent to the domestication.

The tax consequences of the domestication are complex and will depend on a holder’s particular circumstances. All holders are strongly urged to consult their tax advisor for a full description and understanding of the tax consequences of the domestication, including the applicability and effect of U.S. federal, state, local and foreign income and other tax laws. For a more complete discussion of the U.S. federal income tax considerations of the domestication, see “ U.S. Federal Income Tax Considerations ” beginning on page 163 of this joint proxy statement/prospectus.

The existence of financial and personal interests of one or more of GPIA’s directors may result in a conflict of interest on the part of such director(s) between what he or they may believe is in the best interests of GPIA and its shareholders and what he or they may believe is best for himself or themselves in determining to recommend that shareholders vote for the proposals. See the section entitled “ GPIA Business Combination Proposal—Interests of GPIA’s Directors and Officers in the Business Combination ” for a further discussion of this.

On May 16, 2017, in connection with the transactions contemplated by the merger agreement, GPIAC, LLC entered into a transaction support and voting agreement with GPIA and Rimini Street, pursuant to which, among other things, GPIAC, LLC agreed to vote its GPIA ordinary shares in favor of the transactions at the extraordinary general meeting. As of the date of this joint proxy statement/prospectus, the aggregate number of shares covered by the transaction support and voting agreement entered into by GPIAC, LLC represents 21.3% of the outstanding GPIA ordinary shares.

In addition, our independent directors have indicated that they intend to vote their shares in favor of all other proposals being presented at the extraordinary general meeting. As of the date of this joint proxy statement/prospectus, our independent directors own 0.3% of the outstanding GPIA ordinary shares.

At any time prior to the extraordinary general meeting, during a period when they are not then aware of any material nonpublic information regarding GPIA or its securities, the GPIA initial shareholders, Rimini Street and/or its affiliates may purchase shares from institutional and other investors who vote, or indicate an intention to vote, against the business combination proposal, or execute agreements to purchase such shares from such investors in the future, or they may enter into transactions with such investors and others to provide them with incentives to acquire shares of GPIA’s ordinary shares or vote their shares in favor of the business combination proposal. The purpose of such share purchases and other transactions would be to increase the likelihood of satisfaction of the requirements that (i) holders of a majority of the shares who, being present and entitled to vote at the extraordinary general meeting and who do vote, vote in favor of the business combination proposal, the stock issuance proposal and the adjournment proposal, (ii) holders of at least two-thirds of the shares who, being present and entitled to vote at the extraordinary general meeting and who do vote, vote in favor of the domestication proposal and the organizational documents proposals, and (iii) the minimum available cash condition of $50,000,000 and the condition that the minimum trust account balance of $5,000,001 are satisfied. Any such share purchases and other transactions may thereby increase the likelihood of obtaining shareholder approval of the business combination. This may result in the completion of our business combination that may not otherwise have been possible. While the exact nature of any such incentives has not been determined as of the date of this joint proxy statement/prospectus, they might include, without limitation, arrangements to protect such investors or holders against potential loss in value of their shares, including the granting of put options and the transfer to such investors or holders of shares or rights owned by the GPIA initial shareholders for nominal value.

Entering into any such arrangements may have a depressive effect on GPIA’s ordinary shares. For example, as a result of these arrangements, an investor or holder may have the ability to effectively purchase shares at a price lower than market and may therefore be more likely to sell the shares he owns, either prior to or immediately after the extraordinary general meeting. Moreover, any such purchases may make it more likely that the minimum available cash condition of $50,000,000 and the condition that the minimum trust account balance of $5,000,001 are satisfied.

If such transactions are effected, the consequence could be to cause the merger to be approved in circumstances where such approval could not otherwise be obtained. Purchases of shares by the persons described above would allow them to exert more influence over the approval of the proposals to be presented at the extraordinary general meeting and would likely increase the chances that such proposals would be approved. As of the date of this joint proxy statement/prospectus, there have been no such discussions and no agreements to such effect have been entered into with any such investor or holder. GPIA will file a Current Report on Form 8-K to disclose any arrangements entered into or significant purchases made by any of the aforementioned persons that would affect the vote on the proposals to be put to the extraordinary general meeting or the redemption threshold. Any such report will include descriptions of any arrangements entered into or significant purchases by any of the aforementioned persons.

Rimini Street. If you fail to take any action with respect to the extraordinary general meeting and the business combination is not approved, you will remain a shareholder and/or warrant holder of GPIA. However, if you fail to take any action with respect to the extraordinary general meeting, you will nonetheless be able to elect to redeem your public shares in connection with the business combination.

Holders of GPIA public shares should complete the procedures for electing to redeem their GPIA public shares in the manner described above prior to 5:00 p.m. Eastern Time on [ • ], 2017 (two business days before the extraordinary general meeting).

GPIA warrant holders should not submit the certificates relating to their warrants. Public shareholders who do not elect to have their RMNI public shares redeemed for the pro rata share of the trust account should not submit the certificates relating to their public shares.

Upon the domestication, holders of GPIA units, common stock and warrants will receive units, common stock and warrants in RMNI without needing to take any action and accordingly such holders should not submit the certificates relating to their units, common stock and warrants.

Morrow Sodali LLC
470 West Avenue
Stamford CT 06902
Tel: (800) 662-5200
Banks and brokers call collect: (203) 658-9400
E-mail: GPIA.info@morrowsodali.com

You also may obtain additional information about GPIA from documents filed with the SEC by following the instructions in the section entitled “ Where You Can Find More Information; Incorporation by Reference ”. If you are a holder of public shares and you intend to seek redemption of your shares, you will need to deliver your ordinary shares (either physically or electronically) to Continental Stock Transfer & Trust Company, GPIA’s transfer agent, at the address below prior to the extraordinary general meeting. Holders of GPIA public shares should complete the procedures for electing to redeem their GPIA public shares in the manner described above prior to 5:00 p.m. Eastern Time on [ • ], 2017 (two business days before the extraordinary general meeting). If you have questions regarding the certification of your position or delivery of your stock, please contact:

Mark Zimkind
Continental Stock Transfer & Trust Company
1 State Street Plaza, 30th Floor
New York, New York 10004
E-mail: mzimkind@continentalstock.com

QUESTIONS AND ANSWERS FOR STOCKHOLDERS OF RIMINI STREET

Rimini Street will hold the special meeting of its stockholders to consider and vote upon these proposals. This joint proxy statement/prospectus contains important information about the proposed business combination and the other matters to be acted upon at the special meeting. Stockholders of Rimini Street should read it carefully.

After careful consideration, Rimini Street’s board of directors has determined that the Rimini Street business combination proposal and the Rimini Street preferred stock conversion proposal are in the best interests of Rimini Street and its stockholders and recommends that you vote or give instruction to vote “FOR” each of those proposals.

The existence of financial and personal interests of one or more of Rimini Street’s directors may result in a conflict of interest on the part of such director(s) between what he, she or they may believe is in the best interests of Rimini Street and its stockholders and what he, she or they may believe is best for himself, herself or themselves in determining to recommend that stockholders vote for the proposals. See the section entitled “ Rimini Street Business Combination Proposal—Interests of Rimini Street’s Directors and Officers in the Business Combination ” for a further discussion of this.

THE VOTE OF RIMINI STREET STOCKHOLDERS IS IMPORTANT. RIMINI STREET STOCKHOLDERS ARE ENCOURAGED TO VOTE AS SOON AS POSSIBLE AFTER CAREFULLY REVIEWING THIS JOINT PROXY STATEMENT/PROSPECTUS.

statement/prospectus. Upon effectiveness of the business combination, any Rimini Street stockholder who has perfected its dissenters’ rights and who believes that the merger consideration is insufficient will have the right to object and have a court in Nevada determine the value of each share of stock, and to be paid the appraised value determined by the court, which could be more or less than the merger consideration.

For a more complete discussion of the U.S. federal income tax consequences of the mergers, see the section entitled “ U.S. Federal Income Tax Considerations ”.

The existence of financial and personal interests of one or more of Rimini Street’s directors may result in a conflict of interest on the part of such director(s) between what he, she or they may believe is in the best interests of Rimini Street and its stockholders and what he, she or they may believe is best for himself, herself or themselves in determining to recommend that stockholders vote for the proposals. See the section entitled “ Rimini Street Business Combination Proposal—Interests of Rimini Street’s Directors and Officers in the Business Combination ” for a further discussion of this.

Thomas C. Shay
Corporate Secretary
Rimini Street, Inc.
3993 Howard Hughes Parkway, Suite 500
Las Vegas, NV 89169
Tel: (702) 839-9671

who exercise redemption rights and to pay expenses incurred by GPIA and Rimini Street in connection with the business combination. Such expenses include, among others (i) a fee to the underwriters of our initial public offering of $6,037,500, (ii) fees and expenses payable to our investment banking advisors for merger and acquisition advisory services of approximately $9.5 million and (iii) professional fees and expenses of our consultants, accountants and legal counsel of approximately $7.8 million. Any remaining balance in the trust account would thereafter be available for general corporate purposes, including, but not limited to, the prepayment of amounts owed under the Credit Facility and to provide working capital for operations.

In order to consummate the business combination, Rimini Street was required to obtain the consent of a majority of the lenders under the Credit Facility. Certain waiver letters, dated as of May 16, 2017, agreed to by Rimini Street and the agents and lenders provide for consent by the agents and lenders to consummate the business combination. The waiver letters also provide for the waiver of certain events of default under the Credit Facility that may arise as a result of the consummation of the business combination. As a condition to effectiveness of the waiver letters, Rimini Street is required to make a minimum payment to the lenders of $35.0 million to reduce certain outstanding obligations under the Credit Facility.

Prior to consummation of the business combination, Rimini Street and GPIA may jointly elect to offer the lenders under the Credit Facility the ability to convert up to $21.0 million of obligations under the Credit Facility at $10.00 per share for 2,100,000 GPIA ordinary shares, effective immediately prior to the first merger. If Rimini Street and GPIA elect to make this offer, the lenders under the Credit Facility are under no obligation to accept it.

GPIA’s units, ordinary shares and warrants are listed on NASDAQ under the symbols “GPIAU”, “GPIA”, and “GPIAW”, respectively.

The mailing address of GPIA’s principal executive office is 150 E. 52nd Street, Suite 5003, New York, NY 10022. Its telephone number is (212) 430-4340.

Let’s Go Acquisition Corp.

Let’s Go is a wholly-owned subsidiary of GPIA formed solely for the purpose of effecting a business combination. Let’s Go was incorporated under the laws of the State of Delaware on April 13, 2016. Let’s Go owns no material assets and does not operate any business. Pursuant to the first merger, Let’s Go will merge with and into Rimini Street, with Rimini Street as the surviving corporation. Therefore, upon consummation of the first merger, Let’s Go will cease to exist.

The mailing address of Let’s Go’s principal executive office is 150 E. 52nd Street, Suite 5003, New York, NY 10022. Its telephone number is (212) 430-4340.

After consummation of the first merger, Let’s Go will cease to exist.

Rimini Street, Inc.

Rimini Street, founded in 2005, is a global provider of enterprise software products and services, and the leading independent support provider for Oracle and SAP products, based on the number of clients supported. Rimini Street provides subscription-based support services for software products licensed by Oracle Corporation, SAP SE and other software vendors.

For the three months ended March 31, 2017, Rimini Street reported net revenue exceeding $49 million. Rimini Street employs approximately 900 professionals across 13 countries of operation, and currently serves over 1,200 clients – including nearly 100 of the Fortune 500 and Global 100.

Rimini Street’s principal executive offices are at 3993 Howard Hughes Parkway, Suite 500, Las Vegas, Nevada 89169. Rimini Street’s telephone number is (702) 839-9671 and its website is www.riministreet.com.

Information contained on Rimini Street’s website is not incorporated by reference into this joint proxy statement/prospectus and does not constitute part of this joint proxy statement/prospectus.

Emerging Growth Company

GPIA is an “emerging growth company”, as defined in Section 2(a) of the Securities Act, as modified by the Jumpstart Our Business Startups Act of 2012, (the “JOBS Act”), and it may take advantage of certain exemptions from various reporting requirements that are applicable to other public companies that are not emerging growth

companies, including, but not limited to, not being required to comply with the auditor attestation requirements of Section 404 of the Sarbanes-Oxley Act of 2002 (the “Sarbanes-Oxley Act”), reduced disclosure obligations regarding executive compensation in our periodic reports and proxy statements, and exemptions from the requirements of holding a nonbinding advisory vote on executive compensation and stockholder approval of any golden parachute payments not previously approved.

Further, section 102(b)(1) of the JOBS Act exempts emerging growth companies from being required to comply with new or revised financial accounting standards until private companies (that is, those that have not had a Securities Act registration statement declared effective or do not have a class of securities registered under the Exchange Act) are required to comply with the new or revised financial accounting standards. The JOBS Act provides that a company can elect to opt out of the extended transition period and comply with the requirements that apply to non-emerging growth companies but any such election to opt out is irrevocable. GPIA has elected not to opt out of such extended transition period, which means that when a standard is issued or revised and it has different application dates for public or private companies, GPIA, as an emerging growth company, can adopt the new or revised standard at the time private companies adopt the new or revised standard. This may make comparison of GPIA’s financial statements with certain other public companies difficult or impossible because of the potential differences in accounting standards used.

We will remain an emerging growth company until the earlier of (1) the last day of the fiscal year (a) following the fifth anniversary of the completion of our initial public offering (which would be December 31, 2020), (b) in which we have total annual gross revenue of at least $1.07 billion, or (c) in which we are deemed to be a large accelerated filer, which means the market value of our ordinary shares that is held by non-affiliates exceeds $700 million as of the prior June 30 (whichever of (a), (b) or (c) occurs first), and (2) the date on which we have issued more than $1.0 billion in non-convertible debt during the prior three-year period.

Summary of the Merger Agreement

On May 16, 2017, GPIA, Let’s Go, Rimini Street and the Holder Representative entered into the merger agreement, which was amended on June 30, 2017. Pursuant to the merger agreement, among other things and in accordance with the terms and subject to the conditions of the merger agreement, and following the domestication of GPIA to Delaware, Let’s Go, will merge with and into Rimini Street, with Rimini Street as the surviving corporation (which we refer to as the first merger). The surviving corporation from the first merger will then merge with and into GPIA, with GPIA as the surviving corporation (which we refer to as the second merger). See “ GPIA Business Combination Proposal ”.

Prior to and as a condition of the mergers, GPIA will change its jurisdiction of incorporation by effecting a deregistration under Article 206 of the Cayman Islands Companies Law and a domestication under Section 388 of the DGCL, pursuant to which GPIA’s jurisdiction of incorporation will be changed from the Cayman Islands to the State of Delaware. The mergers will follow the domestication.

Merger Consideration

Pursuant to the merger agreement, the aggregate purchase price is $775,000,000, as adjusted in accordance with the terms of the merger agreement (which we refer to as the merger consideration). At the closing of the business combination, GPIA will pay the merger consideration in newly issued shares of RMNI common stock based on a per share issue price of $10.00 per share.

Under the merger agreement, at the effective time of the first merger (the “first effective time”), each issued and outstanding share of Rimini Street’s Class A Common Stock, Class B Common Stock, Series A Preferred Stock on an as-converted basis, Series B Preferred Stock on an as-converted basis and Series C Preferred Stock on an as-converted basis (other than, in each case, such shares, if any, (i) held in the treasury of Rimini Street, which treasury shares shall be canceled as part of the first merger and (ii) shares that are held by stockholders who have perfected and not withdrawn a demand for appraisal rights) will automatically be cancelled and converted into and become the right to receive the applicable portion of the merger consideration in accordance with the merger agreement.

Each option to purchase shares of Rimini Street’s common stock granted under an incentive plan that is outstanding at the first effective time will be converted into an option relating to shares of RMNI (a “RMNI option”) upon the same terms and conditions as are in effect with respect to such option immediately prior to the first effective

time (except that the number of shares of RMNI subject to each RMNI option, and the exercise price thereof, shall be adjusted as set forth in the merger agreement to provide the holder thereof with the same economic value as the original option relating to shares of Rimini Street’s common stock). Rimini Street will take commercially reasonable actions so that any vested option held by a former employee or former service provider to Rimini Street is exercised or cancelled prior to the first effective time and, to the extent not exercised or cancelled, such option will be converted into the right to receive a cash payment equal to the product of (a) the excess of $10 over the per share exercise price and (b) the number of shares of the Rimini Street’s common stock subject to the vested portion of such option. As of May 31, 2017, we estimate that such cash payment would be approximately $161,000. The arrangements described in this paragraph are expected to result in the issuance of RMNI options and warrants relating to 15,637,834 shares of RMNI common stock, representing approximately 15.6% of RMNI’s common stock on a fully-diluted basis immediately following consummation of the business combination (assuming (i) that RMNI issues 50,183,837 shares of RMNI common stock to the former equityholders of Rimini Street pursuant to the merger agreement and that, at consummation of the business combination, there will be outstanding RMNI options and warrants held by former holders of Rimini Street options and warrants, pursuant to which up to 15,637,834 shares of RMNI common stock will be issuable in accordance with the terms of such RMNI options and warrants, (ii) that the Sponsor does not subscribe for any common shares pursuant to its equity commitment at or prior to the consummation of the business combination and (iii) that no public shareholders exercise their redemption rights).

We have entered into a warrant consent and conversion agreement, dated May 16, 2017, with Rimini Street and CB Agent Services LLC (the “Origination Agent”). Pursuant to the warrant consent and conversion agreement, the Origination Agent warrant (as defined below) will be converted into a warrant relating to shares of RMNI. The warrants relating to such warrant consent and conversion agreement are expected to result in warrants relating to 3,537,412 shares of RMNI common stock being issued, representing approximately 20.5% of the total outstanding common stock of RMNI immediately following consummation of the business combination (assuming (i) that RMNI issues 50,183,837 shares of RMNI common stock to the former equityholders of Rimini Street pursuant to the merger agreement and that, at consummation of the business combination, there will be outstanding RMNI options and warrants held by former holders of Rimini Street options and warrants, pursuant to which up to 15,637,834 shares of RMNI common stock will be issuable in accordance with the terms of such RMNI options and warrants, (ii) that the Sponsor does not subscribe for any common shares pursuant to its equity commitment at or prior to the consummation of the business combination and (iii) that no public shareholders exercise their redemption rights). See the section entitled “— Warrant Consent and Conversion Agreement ” for a further discussion of this. All other warrants to purchase shares of Rimini Street’s capital stock, which have an exercise price less than the value of merger consideration per fully diluted share, will be converted into shares of the applicable class of Rimini Street capital stock immediately prior to the first merger, in each case pursuant to a conversion agreement to be agreed with the holders of such warrants and the parties to the merger agreement.

The consummation of the mergers is subject to, among other things, a closing condition requiring a minimum of $50,000,000 of available cash, which is expected to be funded from cash available in the GPIA trust account (after satisfying any shareholder redemptions, but including certain deferred underwriting commissions and other fees) and, as needed, backstop equity financing from GPIC, Ltd. (which we refer to as the Sponsor) of up to $35,000,000 as described below, and other potential third party equity financing (collectively, “GPIA available cash”). Assuming such closing condition is satisfied (and the satisfaction or waiver of the other closing conditions described below), GPIA intends to use the GPIA available cash to fund unpaid transaction expenses incurred in connection with the mergers and the other transactions contemplated by the merger agreement, to pay down certain of Rimini Street’s indebtedness and to deposit any remaining GPIA available cash for the benefit of the combined company’s balance sheet.

The amendment, modification or waiver of the merger agreement in any manner that could reasonably be expected to be materially adverse to Rimini Street or the agents and lenders under the Credit Facility requires the prior written consent of the Origination Agent. There can be no assurance that GPIA, Let’s Go and Rimini Street would waive any such provision of the merger agreement, or that the agents and lenders under the Credit Facility would provide any required consents to such amendments, modifications or waivers.

Merger Agreement Amendment

On June 30, 2017, GPIA, Let’s Go, Rimini Street and the Holder Representative entered into amendment no. 1 to the merger agreement. Pursuant to the merger agreement amendment, the parties agreed to, among other things: (1) amend the provision of the merger agreement relating to cash payments to be made to former employees and

former service providers of Rimini Street who hold outstanding options that have not been exercised by the first effective time, (2) update the capitalization of GPIA referred to in the merger agreement to reflect the number of public shares redeemed by GPIA on May 25, 2017, (3) provide that the mutual closing condition requiring a minimum of $50,000,000 of GPIA available cash includes (rather than excludes) the amount of $6,037,500 that will be paid in respect of deferred underwriting commissions, and (4) delete the provision of the merger agreement requiring GPIA to adopt an employee stock purchase plan.

Equity Commitment

We have entered into an equity commitment letter, dated May 16, 2017, with the Sponsor (the “equity commitment letter”). Pursuant to the equity commitment letter, the Sponsor will (in certain circumstances) provide backstop equity financing by means of purchasing newly issued GPIA ordinary shares based on a per share issue price of $10.00 per share in an aggregate amount of up to $35,000,000 (the “equity commitment”).

If, upon the effectiveness of the first merger, the sum of (i) the cash available in the trust account (after the deduction of the cash used for redemptions of our ordinary shares in connection with the business combination, and including an aggregate of $6,037,500 of deferred underwriting commissions and other fees held in the trust account) and (ii) the cash available to GPIA from the consummation of certain issuances of GPIA ordinary shares (the “non-Sponsor available cash”) is greater than or equal to $50,000,000, then the Sponsor’s equity commitment is zero.

If, upon the effectiveness of the first merger, the non-Sponsor available cash is less than $50,000,000, then the Sponsor’s equity commitment is the lesser of (i) $50,000,000 minus the non-Sponsor available cash and (ii) $35,000,000, which is the maximum commitment of the Sponsor under the equity commitment letter (such amount as calculated pursuant to the foregoing clauses (i) and (ii) being referred to in this joint proxy statement/prospectus as the “commitment”). In addition, pursuant to the equity commitment letter, the Sponsor may, in its sole discretion and in connection with the consummation of the business combination, elect to purchase (on or prior to the domestication) GPIA common shares at a price of $10.00 per share in excess of such commitment, but in all cases up to a maximum of $35,000,000 when aggregated with such commitment.

Therefore, the maximum number of GPIA ordinary shares that the Sponsor can be required to acquire pursuant to the equity commitment letter is 3,500,000 GPIA ordinary shares at a cash purchase price of $10.00 per share. Any GPIA ordinary shares to be acquired by the Sponsor pursuant to the equity commitment letter shall be acquired by the Sponsor upon or prior to the domestication of GPIA as a Delaware corporation.

For more information on the Sponsor’s equity commitment, see “ GPIA Business Combination Proposal—Related Agreements—Equity Commitment Letter ”.

Warrant Consent and Conversion Agreement

Rimini Street and the Origination Agent are party to a warrant purchase agreement (the “Origination Agent warrant agreement”), dated as of June 24, 2016, pursuant to which Rimini Street issued to the Origination Agent certain warrants (collectively the “Origination Agent warrants”) to purchase an aggregate of 14,110,259 shares of Rimini Street common stock at an exercise price per share of $1.35, upon the terms and subject to the conditions set forth in the Origination Agent warrant agreement.

In connection with the mergers, GPIA and Rimini Street have agreed to increase the aggregate number of shares of Rimini Street common stock issuable under the Origination Agent warrant agreement to include an additional 260,000 shares of Rimini Street common stock at an exercise price per share of $1.35 in full satisfaction of a provision of the Origination Agent warrant agreement. Such provision had required Rimini Street, under certain circumstances, to issue to holders of the Origination Agent warrants additional warrants to purchase a number of shares necessary to ensure that such holders hold 5% of Rimini Street’s fully-diluted share capital.

We have entered into a warrant consent and conversion agreement, dated May 16, 2017, by and among GPIA, Rimini Street and the Origination Agent. Pursuant to the warrant consent and conversion agreement, among other things, the Origination Agent agrees immediately prior to, and contingent upon the occurrence of, the first effective time, to: (i) terminate the Origination Agent warrant agreement, (ii) surrender to Rimini Street any and all of its Origination Agent warrants and (iii) receive warrants relating to shares of RMNI. At the consummation of the business combination, GPIA has agreed to issue to the holders of the Origination Agent warrants and each such holder has agreed to convert their relevant allocated portion of Origination Agent warrants into warrants to purchase shares

of RMNI. After such conversion, the Origination Agent warrants will be cancelled and cease to represent a right to acquire shares of Rimini Street common stock. The total number of Origination Agent warrants that will be converted and cancelled is expected to result in warrants relating to 3,537,412 shares of RMNI common stock being issued.

Proposals to be Put to the Shareholders of GPIA at the Extraordinary General Meeting

The following is a summary of the proposals to be put to the extraordinary general meeting of the shareholders of GPIA.

GPIA Business Combination Proposal

The merger agreement provides for a business transaction combination pursuant to which, among other things and in accordance with the terms and subject to the conditions of the merger agreement, and following the domestication of GPIA to Delaware, Let’s Go will merge with and into Rimini Street, with Rimini Street as the surviving corporation (which we refer to as the first merger). The surviving corporation from the first merger will then merge with and into GPIA, with GPIA as the surviving corporation (which we refer to as the second merger). Prior to and as a condition of the mergers, GPIA will change its jurisdiction of incorporation by effecting a deregistration under Article 206 of the Cayman Islands Companies Law and a domestication under Section 388 of the DGCL, pursuant to which GPIA’s jurisdiction of incorporation will be changed from the Cayman Islands to the State of Delaware. The mergers will follow the domestication.

The aggregate merger consideration is $775 million, subject to certain adjustments identified in the merger agreement, and is payable entirely in newly issued common stock of RMNI based on a per share issue price of $10.00 per share.

After consideration of the factors identified and discussed in the section entitled “ GPIA Business Combination Proposal—GPIA’s Board of Directors’ and the Special Transaction Committee’s Reasons for the Business Combination ”, GPIA’s board of directors concluded that the business combination met all of the requirements disclosed in the prospectus for its initial public offering, including that the business of Rimini Street had a fair market value of at least 80% of the balance of the funds in the trust account at the time of execution of the merger agreement.

If any proposal is not approved by GPIA’s shareholders at the extraordinary general meeting, the GPIA board of directors may submit the adjournment proposal for a vote.

For additional information, see “ GPIA Business Combination Proposal ” section of this joint proxy statement/prospectus.

GPIA Domestication Proposal

As discussed in this joint proxy statement/prospectus, if the business combination proposal is approved, then GPIA is asking its shareholders to approve the domestication proposal. Under the merger agreement, the approval of the domestication proposal is also a condition to the consummation of the business combination. If, however, the domestication proposal is approved, but the business combination proposal is not approved, then neither the domestication nor the business combination will be consummated.

As a condition to closing the business combination pursuant to the terms of the merger agreement, the board of directors of GPIA has unanimously approved a change of GPIA’s jurisdiction of incorporation by deregistering as an exempted company in the Cayman Islands and continuing and domesticating as a corporation incorporated under the laws of the State of Delaware (the “domestication”). To effect the domestication, GPIA will file a notice of deregistration with the Cayman Islands Registrar of Companies, together with the necessary accompanying documents, and file a certificate of incorporation and a certificate of corporate domestication with the Secretary of State of the State of Delaware, under which GPIA will be domesticated and continue as a Delaware corporation. On the effective date of the domestication, each currently issued and outstanding ordinary share, par value $0.0001 per share, of GPIA will convert automatically by operation of law, on a one-for-one basis, into shares of common stock, par value $0.0001 per share, of GP Investments Acquisition Corp. (after its domestication as a corporation incorporated in the State of Delaware), which will be renamed “Rimini Street, Inc.” immediately after consummation of the second merger. Similarly, outstanding warrants of GPIA will become warrants to acquire the corresponding shares of RMNI common stock and no other changes will be made to the terms of any outstanding warrants as a result of the domestication.

The domestication proposal, if approved, will approve a change of GPIA’s jurisdiction of incorporation from the Cayman Islands to the State of Delaware. Accordingly, while GPIA is currently governed by the Cayman Islands Companies Law, upon domestication, RMNI will be governed by the DGCL. Accordingly, we encourage shareholders to carefully consult the information set out below under “ Comparison of Corporate Governance and Shareholder Rights ”. Additionally, we note that if the domestication proposal is approved, then GPIA will also ask its shareholders to approve the organizational documents proposals (discussed below) and we encourage shareholders to carefully consult the section entitled “ GPIA Organizational Documents Proposals ” (including the chart of material differences included therein) and the Proposed Organizational Documents of RMNI, attached hereto as Annexes C and D.

For additional information, see “ GPIA Domestication Proposal ” section of this joint proxy statement/prospectus.

GPIA Organizational Documents Proposals

If the domestication proposal is approved and the business combination is to be consummated, GPIA will replace the current amended and restated memorandum of association of GPIA under the Cayman Islands Companies Law (the “Existing Memorandum”) and the current articles of association of GPIA (the “Existing Articles” and, together with the Existing Memorandum, the “Existing Organizational Documents”), in each case, under the Cayman Islands Companies Law, with a new certificate of incorporation (the “Proposed Charter”) and bylaws (the “Proposed Bylaws” and, together with the Proposed Charter, the “Proposed Organizational Documents”) of RMNI, in each case, under the Delaware General Corporation Law.

The Proposed Organizational Documents differ in certain material respects from the Existing Organizational Documents and we encourage shareholders to carefully consult the information set out in the Section “ GPIA Organizational Documents Proposals ” (including the chart of material differences included therein) and the full text of the Proposed Organizational Documents of RMNI, attached hereto as Annexes C and D.

GPIA’s shareholders are asked to consider and vote upon and to approve by special resolution seven separate proposals (collectively, the “organizational documents proposals”) in connection with the replacement of the Existing Organizational Documents with the Proposed Organizational Documents. The organizational documents proposals are conditioned on the approval of the domestication proposal, and, therefore, also conditioned on approval of the business combination proposal. Therefore, if the business combination proposal and the domestication proposal are not approved, the organizational documents proposals will have no effect, even if approved by holders of GPIA ordinary shares. A brief summary of each of the organizational documents proposals is set forth below. These summaries are qualified in their entirety by reference to the complete text of the Proposed Organizational Documents of RMNI.

GPIA Organizational Documents Proposal A—Approval of Authorization of Additional Shares of Common Stock and Preferred Stock of RMNI

Assuming the business combination proposal and the domestication proposal are approved, our shareholders are also being asked to approve organizational documents proposal A, which is, in the judgment of our board of directors, necessary to adequately address the needs of RMNI after the business combination. Under the merger agreement, the approval of each of the organizational documents proposals is a condition to the consummation of the business combination, and therefore, approval of this organizational documents proposal A is a condition to the consummation of the business combination.

As of the date of this joint proxy statement/prospectus, GPIA had 20,009,776 ordinary shares issued and outstanding, consisting of 15,697,276 shares sold as part of the units issued in our initial public offering (being 17,250,000 public shares issued in our initial public offering as reduced by the redemption of 1,552,724 public shares on May 25, 2017 in connection with the Extension) and 4,312,500 founder shares that were issued to the Sponsor prior to our initial public offering. All of the outstanding ordinary shares of GPIA will be converted by operation of law into shares of common stock of RMNI in the domestication.

In connection with the business combination, based on an illustrative Closing Date of May 31, 2017 (being the most recent date for which Rimini Street month end balance sheet data is available prior to the date of this joint proxy statement/prospectus), based on assumptions described elsewhere in this joint proxy statement/prospectus, upon consummation of the first merger the stockholders of Rimini Street immediately prior to consummation of the first

merger will receive 50,183,837 shares of RMNI common stock. In addition, in certain circumstances described elsewhere in this joint proxy statement/prospectus, the Sponsor may subscribe for up to 3,500,000 GPIA ordinary shares pursuant to its equity commitment at or prior to the consummation of the business combination.

In order to ensure that RMNI has sufficient authorized capital for future issuances, our board of directors has approved, subject to stockholder approval, that the Proposed Organizational Documents of RMNI (i) increase the number of shares of our common stock from 400,000,000 ordinary shares (as currently authorized in GPIA’s Existing Organizational Documents), to 1,000,000,000 shares of RMNI common stock (an increase of 600,000,000 shares of common stock), and (ii) increase the number of shares of our preferred stock from 20,000,000 (as currently authorized in GPIA’s Existing Organizational Documents), to 100,000,000 shares of RMNI preferred stock (an increase of 80,000,000 shares of preferred stock).

For additional information, see “ GPIA Organizational Documents Proposal A—Approval of Authorization of Additional Shares of Common Stock and Preferred Stock of RMNI, as Set Forth in the Proposed Organizational Documents ” section of this joint proxy statement/prospectus.

Organizational Documents Proposal B—Approval of Issuance of Preferred Stock of RMNI at the Board of Directors’ Sole Discretion

Assuming the business combination proposal and the domestication proposal are approved, our shareholders are also being asked to approve organizational documents proposal B, which is, in the judgment of our board of directors, necessary to adequately address the needs of RMNI after the business combination. Under the merger agreement, the approval of each of the organizational documents proposals is a condition to the consummation of the business combination, and therefore approval of this organizational documents proposal B is a condition to the consummation of the business combination.

GPIA currently has 20,000,000 shares of preferred stock that, assuming approval of the domestication proposal and RMNI’s incorporation in the State of Delaware, will become 20,000,000 shares of preferred stock of RMNI. In addition, if organizational documents proposal A is approved, the number of authorized shares of preferred stock of RMNI will be increased by 80,000,000 to 100,000,000 shares of preferred stock of RMNI. Approval of this organizational documents proposal B will allow for issuance of any or all of these shares of preferred stock from time to time at the discretion of the board of directors, as may be permitted by the DGCL, and without further stockholder action. The shares of preferred stock would be issuable for any proper corporate purpose, including, among other things, future acquisitions, capital raising transactions consisting of equity or convertible debt, stock dividends or issuances under current and any future stock incentive plans, pursuant to which we may provide equity incentives to employees, officers and directors, and in certain instances may be used as an anti-takeover defense.

For additional information, see “ GPIA Organizational Documents Proposal B—Approval of Proposal Regarding Issuance of Preferred Stock of RMNI at the Board of Directors’ Sole Discretion, as Set Forth in the Proposed Organizational Documents ” section of this joint proxy statement/prospectus.

Organizational Documents Proposal C—Standard Required for Director Removal

Assuming the business combination proposal and the domestication proposal are approved, our shareholders are also being asked to approve organizational documents proposal C, which is, in the judgment of our board of directors, necessary to adequately address the needs of RMNI after the business combination. Under the merger agreement, the approval of each of the organizational documents proposals is a condition to the consummation of the business combination and therefore approval of this organizational documents proposal C is a condition to the consummation of the business combination.

The Proposed Organizational Documents stipulate that any director or the entire board of directors may be removed from office at any time, but only for cause. Additionally, a decrease in the size of the board of directors will not have the effect of removing any incumbent director before his or her term expires.

For additional information, see “ GPIA Organizational Documents Proposal C—Approval of Standard Required For Director Removal, as Set Forth in the Proposed Organizational Documents ” section of this joint proxy statement/prospectus.

Organizational Documents Proposal D—Approval of Proposal Relating to the Ability of Stockholders to Call a Special Meeting

Assuming the business combination proposal and the domestication proposal are approved, our shareholders are also being asked to approve organizational documents proposal D, which is, in the judgment of our board of directors, necessary to adequately address the needs of RMNI after the business combination. Under the merger agreement, the approval of each of the organizational documents proposals is a condition to the consummation of the business combination and therefore, approval of this organizational documents proposal D is a condition to the consummation of the business combination.

The Proposed Organizational Documents stipulate that, unless required by law, special meetings of stockholders may only be called by (i) the RMNI board of directors, (ii) the chairperson of the board of directors, (iii) the chief executive officer of RMNI or (iv) the president of RMNI (in the absence of the chief executive officer). Under the Proposed Organizational Documents, RMNI’s stockholders have no power to call a special meeting.

For additional information, see “ GPIA Organizational Documents Proposal D—Approval of Proposal Regarding the Ability of Stockholders To Call A Special Meeting, as Set Forth in the Proposed Organizational Documents ” section of this joint proxy statement/prospectus.

Organizational Documents Proposal E—Approval of Proposal Relating to the Ability of Stockholders to Act By Written Consent

Assuming the business combination proposal and the domestication proposal are approved, our shareholders are also being asked to approve organizational documents proposal E, which is, in the judgment of our board of directors, necessary to adequately address the needs of RMNI after the business combination. Under the merger agreement, the approval of each of the organizational documents proposals is a condition to the consummation of the business combination and therefore, approval of this organizational documents proposal E is a condition to the consummation of the business combination.

The Proposed Organizational Documents stipulate that any action required or permitted to be taken by the stockholders of RMNI must be effected at a duly called annual or special meeting of stockholders of RMNI, and may not be effected by any consent in writing by such stockholders.

For additional information, see “ GPIA Organizational Documents Proposal E—Approval of Proposal Regarding the Ability of Stockholders To Act By Written Consent, as Set Forth in the Proposed Organizational Documents ” section of this joint proxy statement/prospectus.

Organizational Documents Proposal F—Approval of Threshold for Stockholder Vote to Amend to the Certificate of Incorporation and Bylaws of RMNI

Assuming the business combination proposal and the domestication proposal are approved, our shareholders are also being asked to approve organizational documents proposal F, which is, in the judgment of our board of directors, necessary to adequately address the needs of RMNI after the business combination. Under the merger agreement, the approval of each of the organizational documents proposals is a condition to the consummation of the business combination and therefore approval of this organizational documents proposal F is a condition to the consummation of the business combination.

The Proposed Organizational Documents stipulate that RMNI reserves the right to amend, alter, change or repeal any provision of its certificate of incorporation. Stockholders of RMNI can amend, alter, change or repeal any provision of RMNI’s certificate of incorporation (other than the articles thereof relating to RMNI’s name, address and registered office, purpose and matters related to RMNI’s common and preferred stock), by the affirmative vote of the holders of at least sixty-six and two-thirds percent (66 2/3%) of the voting power of RMNI’s then outstanding capital stock entitled to vote generally in the election of directors, voting together as a single class.

The Proposed Organizational Documents also stipulate that RMNI’s bylaws may be amended, altered or repealed by the affirmative vote of the holders of at least sixty-six and two-thirds percent (66 2/3%) of the voting power of RMNI’s then outstanding capital stock entitled to vote generally in the election of directors, voting together as a single class. This provision is in addition to the ability of RMNI’s board of directors to take such action by the affirmative vote of at least a majority of the entire board of directors.

For additional information, see “ GPIA Organizational Documents Proposal F—Approval of Threshold for Stockholder Vote to Amend (1) Certain Provisions of the Certificate of incorporation and (2) the Bylaws of RMNI, as Set Forth in the Proposed Organizational Documents ” section of this joint proxy statement/prospectus.

Organizational Documents Proposal G—Approval of Other Changes in Connection with Adoption of the Proposed Organizational Documents

Assuming the business combination proposal and the domestication proposal are approved, our shareholders are also being asked to approve organizational documents proposal G, which is, in the judgment of our board of directors, necessary to adequately address the needs of RMNI after the business combination. Under the merger agreement, the approval of each of the organizational documents proposals is a condition to the consummation of the business combination and therefore, approval of this organizational documents proposal G is a condition to the consummation of the business combination.

Organizational documents proposal G is a proposal to authorize all other changes in connection with the replacement of our memorandum and articles of association with a new certificate of incorporation and bylaws of RMNI as part of the domestication, including (i) changing the post-business combination corporate name from “GP Investments Acquisition Corp.” to “Rimini Street, Inc.” (with such change expected to be made immediately following the consummation of the second merger) and making RMNI’s corporate existence perpetual, (ii) adopting Delaware as the exclusive forum for certain stockholder litigation, and (iii) removing certain provisions related to our status as a blank check company that will no longer apply upon consummation of the business combination, all of which GPIA’s board of directors believe is necessary to adequately address the needs of RMNI after the business combination.

For additional information, see “ GPIA Organizational Documents Proposal G—Approval of Other Changes in Connection With Adoption of the Proposed Organizational Documents ” section of this joint proxy statement/prospectus.

GPIA Stock Issuance Proposal

Assuming the business combination proposal, the domestication proposal and each of the organizational documents proposals are approved, our shareholders are also being asked to approve, by ordinary resolution, the stock issuance proposal.

Our common shares are listed on NASDAQ and, as such, we are seeking shareholder approval of the issuance of RMNI common stock to (1) the existing stockholders of Rimini Street in connection with the business combination and (2) the Sponsor pursuant to its equity commitment in connection with the business combination, to the extent such issuance would require a shareholder vote under NASDAQ Listing Rule 5635, in each case, in order to comply with NASDAQ Listing Rule 5635.

For additional information, see “ GPIA Stock Issuance Proposal ” section of this joint proxy statement/prospectus.

GPIA Adjournment Proposal

If, based on the tabulated vote, there are not sufficient votes at the time of the extraordinary general meeting to authorize GPIA to consummate the business combination (because any of the condition precedent proposals have not been approved (including as a result of the failure of any other cross-conditioned condition precedent proposals to be approved)), GPIA’s board of directors may submit a proposal to adjourn the extraordinary general meeting to a later date or dates, if necessary, to permit further solicitation of proxies.

For additional information, see “ GPIA Adjournment Proposal ” section of this joint proxy statement/prospectus.

GPIA Initial Shareholders

As of the date of this joint proxy statement/prospectus, the Sponsor, GPIC, Ltd., an affiliate of GP Investments, Ltd., owns 4,252,500 ordinary shares, and our independent directors own an aggregate of 60,000 ordinary shares. We refer to the Sponsor and our independent directors that own any of our ordinary shares as our “initial shareholders”, and the 4,312,500 ordinary shares that they own in aggregate are referred to as the “founder shares”. In addition, the

Sponsor owns 6,062,500 warrants (the “private placement warrants”) that were issued in a private placement that closed simultaneously with our initial public offering. In addition, an affiliate of the Sponsor owns 52,100 warrants that were acquired by such affiliate in the secondary market following our initial public offering.

Assuming consummation of the business combination as of May 31, 2017 (being the most recent date for which Rimini Street month end balance sheet data is available prior to the date of this joint proxy statement/prospectus), immediately following the consummation of the business combination (without taking into account any GPIA ordinary shares held by Rimini Street stockholders prior to the consummation of the business combination, and assuming (i) that the Sponsor does not subscribe for any common shares pursuant to its equity commitment at or prior to the consummation of the business combination, (ii) that RMNI issues 50,183,837 shares of RMNI common stock to the former equityholders of Rimini Street pursuant to the merger agreement and that, at consummation of the business combination, there will be outstanding RMNI options and warrants held by former holders of Rimini Street options and warrants, pursuant to which up to 15,637,834 shares of RMNI common stock will be issuable in accordance with the terms of such RMNI options and warrants and (iii) that no public shareholders exercise their redemption rights), the former equityholders of Rimini Street are expected to own approximately 71.5% of RMNI’s common stock (or 65.5% of RMNI’s common stock on a fully-diluted basis) and GPIA’s current shareholders are expected to own approximately 28.5% of RMNI’s common stock (or 34.5% of RMNI’s common stock on a fully-diluted basis), which comprises (i) 6.2% of RMNI’s common stock (or 10.4% of RMNI’s common stock on a fully-diluted basis) expected to be owned by GPIA’s initial shareholders and (ii) 22.4% of RMNI’s common stock (or 24.2% of RMNI’s common stock on a fully-diluted basis) expected to be owned by GPIA’s public shareholders.

Assuming consummation of the business combination as of May 31, 2017 (being the most recent date for which Rimini Street month end balance sheet data is available prior to the date of this joint proxy statement/prospectus), immediately following the consummation of the business combination (without taking into account any GPIA ordinary shares held by Rimini Street stockholders prior to the consummation of the business combination, and assuming (i) that RMNI issues 50,183,837 shares of RMNI common stock to the former equityholders of Rimini Street pursuant to the merger agreement and that, at consummation of the business combination, there will be outstanding RMNI options and warrants held by former holders of Rimini Street options and warrants, pursuant to which up to 15,637,834 shares of RMNI common stock will be issuable in accordance with the terms of such RMNI options and warrants, (ii) that the Sponsor subscribes for 3,500,000 GPIA ordinary shares pursuant to its equity commitment at or prior to the consummation of the business combination and (iii) that holders of 14,205,056 GPIA ordinary shares (or 90.5% of the outstanding public shares) (being our estimate of the maximum number of GPIA public shares that could be redeemed in order for GPIA to have $50,000,000 of available cash upon consummation of the first merger, after taking into account the Sponsor’s maximum equity commitment of $35,000,000) elect to redeem their ordinary shares in connection with the business combination), the former equityholders of Rimini Street are expected to own approximately 84.4% of RMNI’s common stock (or 73.3% of RMNI’s common stock on a fully-diluted basis) and GPIA’s current shareholders are expected to own approximately 15.6% of RMNI’s common stock (or 26.7% of RMNI’s common stock on a fully-diluted basis), which comprises (i) 13.1% of RMNI’s common stock (or 15.5% of RMNI’s common stock on a fully-diluted basis) expected to be owned by GPIA’s initial shareholders and (ii) 2.5% of RMNI’s common stock (or 11.3% of RMNI’s common stock on a fully-diluted basis) expected to be owned by GPIA’s public shareholders.

In connection with our initial public offering, our initial shareholders entered into letter agreements to vote their founder shares, as well as any public shares purchased during or after our initial public offering, in favor of the business combination proposal. In addition, on May 16, 2017, in connection with the transactions contemplated by the merger agreement, GPIAC, LLC entered into a transaction support and voting agreement with GPIA and Rimini Street, pursuant to which, among other things, GPIAC, LLC agreed to vote its GPIA ordinary shares in favor of the transactions at the extraordinary general meeting. As of the date of this joint proxy statement/prospectus, the aggregate number of shares covered by the transaction support and voting agreement entered into by GPIAC, LLC represents 21.3% of the outstanding GPIA ordinary shares. In addition, our independent directors have indicated that they intend to vote their shares in favor of all other proposals being presented at the extraordinary general meeting. As of the date of this joint proxy statement/prospectus, our independent directors own 0.3% of the outstanding GPIA ordinary shares.

In connection with our initial public offering, the founder shares were placed into an escrow account maintained in New York, New York by Continental Stock Transfer & Trust Company, acting as escrow agent. Subject to certain limited exceptions, these founder shares will not be transferred, assigned or sold until released from escrow on the

date that is one year after the date of the consummation of our initial business combination or earlier if, subsequent to our business combination, (i) the last sale price of our ordinary shares equals or exceeds $12.00 per share (as adjusted for share splits, share dividends, reorganizations and recapitalizations) for any 20 trading days within any 30-trading day period commencing at least 150 days after our initial business combination or (ii) we consummate a subsequent liquidation, merger, share exchange or other similar transaction which results in all of our shareholders having the right to exchange their ordinary shares for cash, securities or other property. We refer to such transfer restrictions throughout this joint proxy statement/prospectus as the “lock-up”.

Organizational Structure

The following diagram illustrates the ownership structure of RMNI immediately following consummation of the business combination. This diagram does not take into account any GPIA ordinary shares held by Rimini Street stockholders prior to the consummation of the business combination, is based on an illustrative Closing Date of May 31, 2017 (being the most recent date for which Rimini Street month end balance sheet data is available prior to the date of this joint proxy statement/prospectus) and assumes (i) the Sponsor does not subscribe for any common shares pursuant to its equity commitment at or prior to the consummation of the business combination, (ii) that RMNI issues 50,183,837 shares of RMNI common stock to the former equityholders of Rimini Street pursuant to the merger agreement and (iii) that no public shareholders exercise their redemption rights. If these assumptions are not correct, then the shareholdings set forth in the diagram below would change.

Date, Time and Place of Extraordinary General Meeting of GPIA’s Shareholders

The extraordinary general meeting of the shareholders of GPIA will be held at [•] [a.m.][p.m.], Eastern Time, on [•], 2017, at the offices of Skadden, Arps, Slate, Meagher & Flom LLP at 4 Times Square, New York, New York 10036, to consider and vote upon the proposals to be put to the extraordinary general meeting, including if necessary, the adjournment proposal, to permit further solicitation and vote of proxies if, based upon the tabulated vote at the time of the extraordinary general meeting, each of the condition precedent proposals have not been approved.

Voting Power; Record Date

GPIA shareholders will be entitled to vote or direct votes to be cast at the extraordinary general meeting if they owned GPIA ordinary shares at the close of business on [•], 2017, which is the record date for the extraordinary general meeting. Shareholders will have one vote for each GPIA ordinary share owned at the close of business on the record date. If your shares are held in “street name” or are in a margin or similar account, you should contact your broker to ensure that votes related to the shares you beneficially own are properly counted. Our warrants do not have voting rights. On the record date, there were 20,009,776 GPIA ordinary shares outstanding, of which 15,697,276 were public shares with the rest being held by the GPIA initial shareholders.

Quorum and Vote of GPIA Shareholders

A quorum of GPIA shareholders is necessary to hold a valid meeting. A quorum will be present at the GPIA general meeting if a majority of the outstanding shares entitled to vote at the extraordinary general meeting are represented in person or by proxy. Abstentions and broker non-votes, while considered present for the purposes of establishing a quorum, will not count as votes cast at the extraordinary general meeting.

As of the record date for the extraordinary general meeting, 10,004,889 GPIA ordinary shares would be required to achieve a quorum.

In connection with our initial public offering, our initial shareholders (consisting of the Sponsor and our independent directors at the time of our initial public offering) entered into letter agreements to vote their founder shares, as well as any public shares purchased during or after our initial public offering, in favor of the business combination proposal. In addition, on May 16, 2017, in connection with the transactions contemplated by the merger agreement, GPIAC, LLC entered into a transaction support and voting agreement with GPIA and Rimini Street, pursuant to which, among other things, GPIAC, LLC agreed to vote its GPIA ordinary shares in favor of the transactions at the extraordinary general meeting. As of the date of this joint proxy statement/prospectus, the aggregate number of shares covered by the transaction support and voting agreement entered into by GPIAC, LLC represents 21.3% of the outstanding GPIA ordinary shares. In addition, our independent directors have indicated that they intend to vote their shares in favor of all other proposals being presented at the extraordinary general meeting. As of the date of this joint proxy statement/prospectus, our independent directors own 0.3% of the outstanding GPIA ordinary shares.

The proposals presented at the extraordinary general meeting require the following votes:

Abstentions and broker non-votes, while considered present for the purposes of establishing a quorum, will not count as votes cast at the extraordinary general meeting.

Redemption Rights

Pursuant to our memorandum and articles of association, a public shareholder may request of GPIA that RMNI redeem all or a portion of the RMNI public shares that such public shareholder will hold following the domestication for cash if the business combination is consummated. GP Investments Acquisition Corp. (after its domestication as a corporation incorporated in the State of Delaware) will be the continuing entity following the domestication, which is the entity that survives the mergers (and which will be renamed “Rimini Street, Inc.” immediately after consummation of the second merger). As a change of entity name does not involve a change in the legal form of the

entity, in this joint proxy statement/prospectus, “RMNI” refers to GP Investments Acquisition Corp., a corporation incorporated in the State of Delaware, including subsequent to its change of name to Rimini Street, Inc. Public shareholders will be entitled to receive cash for RMNI public shares only as provided below:

Holders of GPIA public shares should complete the procedures for electing to redeem their GPIA public shares in the manner described above prior to 5:00 p.m. Eastern Time on [ • ], 2017 (two business days before the extraordinary general meeting).

As noted above, holders of units must elect to separate the underlying public shares and public warrants prior to exercising redemption rights with respect to the public shares. Holders may instruct their broker to do so, or if a holder holds units registered in its own name, the holder must contact Continental Stock Transfer & Trust Company, GPIA’s transfer agent, directly and instruct them to do so. Public stockholders may elect to redeem RMNI public shares regardless of if or how they vote in respect of the business combination proposal . If the business combination is not consummated, the public shares will not be redeemed for cash. If a public shareholder properly exercises its right to redeem all or a portion of the RMNI public shares that it will hold upon the domestication and timely delivers its public shares to Continental Stock Transfer & Trust Company, GPIA’s transfer agent, RMNI will redeem such RMNI public shares into a pro rata portion of the trust account, calculated as of two business days prior to the consummation of the business combination. For illustrative purposes, as of May 25, 2017 (after giving effect to the redemptions of public shares redeemed in connection with the Extension), this would have amounted to approximately $10.05 per public share. If a public shareholder exercises its redemption rights, then it will be electing to exchange its GPIA ordinary shares (that become RMNI shares upon the domestication) for cash and will no longer own RMNI public shares. The redemption takes place following the domestication and accordingly it is RMNI public shares that are redeemed immediately after consummation of the second merger. See “ Extraordinary General Meeting of Shareholders of GPIA —Redemption Rights ” for a detailed description of the procedures to be followed if you wish to redeem your RMNI public shares for cash.

Notwithstanding the foregoing, a holder of public shares, together with any affiliate of such public shareholder or any other person with whom such public shareholder is acting in concert or as a “group” (as defined in Section 13(d)(3) of the Exchange Act), will be restricted from redeeming its RMNI public shares with respect to more than an aggregate of 20% of the RMNI public shares. Accordingly, if a public shareholder, alone or acting in concert or as a group, seeks to redeem more than 20% of the public shares, then any such shares in excess of that 20% limit would not be redeemed for cash.

Under the merger agreement, the consummation of the first merger is conditioned upon, among other things, (i) there being a minimum of $50,000,000 of cash available to GPIA (including the cash in our trust account and any cash provided by the Sponsor pursuant to its equity commitment) and (ii) there being a minimum amount of immediately available cash in the trust account of not less than $5,000,001 after giving effect to the redemption of GPIA ordinary shares that holders of GPIA ordinary shares validly elected to redeem in connection with the business combination. Therefore, unless these conditions are waived by GPIA, Let’s Go and Rimini Street, the merger agreement could terminate and the proposed business combination may not be consummated. There can be no assurance that GPIA, Let’s Go and Rimini Street would waive such provisions of the merger agreement. Furthermore, as provided in our memorandum and articles of association, in no event will we redeem our public shares in an amount that would cause our net tangible assets to be less than $5,000,001 (so that we are not subject to the SEC’s “penny stock” rules).

In order for public shareholders to exercise their redemption rights in respect of the proposed business combination, public shareholders must properly exercise their right to redeem the RMNI public shares that you will hold upon the domestication prior to the extraordinary general meeting and deliver their ordinary shares (either

physically or electronically) to Continental Stock Transfer & Trust Company, GPIA’s transfer agent, prior to the extraordinary general meeting. Holders of GPIA public shares should complete the procedures for electing to redeem their GPIA public shares in the manner described above prior to 5:00 p.m. Eastern Time on [ • ], 2017 (two business days before the extraordinary general meeting).

Therefore, the election to exercise redemption rights occurs prior to the domestication and the redemption is with respect to the RMNI public shares that an electing public shareholder holds after the domestication. For the purposes of Article 48.3 of our memorandum and articles of association and the Cayman Islands Companies Law, the exercise of redemption rights shall be treated as an election to have such public shares repurchased for cash and references in this joint proxy statement/prospectus to “redemption” or “redeeming” shall be interpreted accordingly. Immediately following the domestication and the consummation of the business combination, RMNI shall satisfy the exercise of redemption rights by redeeming the RMNI public shares issued to the public shareholders that validly exercised their redemption rights.

Holders of our warrants will not have redemption rights with respect to the warrants.

Appraisal Rights

Neither GPIA shareholders nor GPIA warrant holders have appraisal rights in connection with the business combination or the domestication under the Cayman Islands Companies Law or under the DGCL.

Proxy Solicitation

Proxies may be solicited by mail, telephone or in person. GPIA has engaged Morrow Sodali LLC to assist in the solicitation of proxies.

If a shareholder grants a proxy, it may still vote its shares in person if it revokes its proxy before the extraordinary general meeting. A shareholder also may change its vote by submitting a later-dated proxy as described in the section entitled “ Special Meeting of GPIA Shareholders—Revoking Your Proxy ”.

Interests of GPIA’s Directors and Officers in the Business Combination

When you consider the recommendation of GPIA’s board of directors in favor of approval of the business combination proposal, you should keep in mind that GPIA’s initial shareholders, including its directors and executive officers, have interests in such proposal that are different from, or in addition to, those of GPIA shareholders and warrant holders generally. These interests include, among other things, the interests listed below:

At any time prior to the extraordinary general meeting, during a period when they are not then aware of any material nonpublic information regarding GPIA or its securities, the GPIA initial shareholders, Rimini Street and/or its affiliates may purchase shares from institutional and other investors who vote, or indicate an intention to vote, against the business combination proposal, or execute agreements to purchase such shares from such investors in the future, or they may enter into transactions with such investors and others to provide them with incentives to acquire shares of GPIA’s ordinary shares or vote their shares in favor of the business combination proposal. The purpose of such share purchases and other transactions would be to increase the likelihood of satisfaction of the requirements that (i) holders of a majority of the shares who, being present and entitled to vote at the extraordinary general meeting and who do vote, vote in favor of the business combination proposal, the stock issuance proposal and the adjournment proposal, (ii) holders of at least two-thirds of the share who, being present and entitled to vote at the extraordinary general meeting and who do vote, vote in favor of the domestication proposal and the organizational documents proposals, and (iii) the minimum available cash condition of $50,000,000 and the condition that the minimum trust account balance of $5,000,001 are satisfied. Any such share purchases and other transactions may thereby increase the likelihood of obtaining shareholder approval of the business combination. This may result in the completion of our business combination that may not otherwise have been possible. While the exact nature of any such incentives

has not been determined as of the date of this joint proxy statement/prospectus, they might include, without limitation, arrangements to protect such investors or holders against potential loss in value of their shares, including the granting of put options and the transfer to such investors or holders of shares or rights owned by the GPIA initial shareholders for nominal value.

Entering into any such arrangements may have a depressive effect on GPIA’s ordinary shares. For example, as a result of these arrangements, an investor or holder may have the ability to effectively purchase shares at a price lower than market and may therefore be more likely to sell the shares he owns, either prior to or immediately after the extraordinary general meeting. Moreover, any such purchases may make it more likely that the minimum available cash condition of $50,000,000 and the condition that the minimum trust account balance of $5,000,001 are satisfied.

If such transactions are effected, the consequence could be to cause the business combination to be approved in circumstances where such approval could not otherwise be obtained. Purchases of shares by the persons described above would allow them to exert more influence over the approval of the proposal to be presented at the extraordinary general meeting and would likely increase the chances that such proposals would be approved. As of the date of this joint proxy statement/prospectus, there have been no such discussions and no agreements to such effect have been entered into with any such investor or holder. GPIA will file a Current Report on Form 8-K to disclose any arrangements entered into or significant purchases made by any of the aforementioned persons that would affect the vote on the proposals to be put to the extraordinary general meeting or the redemption threshold. Any such report will include descriptions of any arrangements entered into or significant purchases by any of the aforementioned persons.

The existence of financial and personal interests of one or more of GPIA’s directors may result in a conflict of interest on the part of such director(s) between what he or they may believe is best for GPIA and what he or they may believe is best for himself or themselves in determining to recommend that shareholders vote for the proposals. See the sections entitled “ Risk Factors ” and “ GPIA Business Combination Proposal—Interests of GPIA’s Directors and Officers in the Business Combination ” for a further discussion of this and other risks.

Recommendation to Shareholders of GPIA

GPIA’s board of directors believes that the business combination proposal and the other proposals to be presented at the extraordinary general meeting are in the best interest of GPIA’s shareholders and unanimously recommends that its shareholders vote “FOR” the business combination proposal, “FOR” the domestication proposal, “FOR” each of the separate organizational documents proposals, “FOR” the stock issuance proposal and “FOR” the adjournment proposal, in each case, if presented to the extraordinary general meeting.

The existence of financial and personal interests of one or more of GPIA’s directors may result in a conflict of interest on the part of such director(s) between what he or they may believe is in the best interests of GPIA and its shareholders and what he or they may believe is best for himself or themselves in determining to recommend that shareholders vote for the proposals. See the section entitled “ GPIA Business Combination Proposal—Interests of GPIA’s Directors and Officers in the Business Combination ” for a further discussion of this.

Proposals to be Put to the Stockholders of Rimini Street at the Special Meeting

The following is a summary of the proposals to be put to the special meeting of stockholders of Rimini Street.

Rimini Street Business Combination Proposal

The merger agreement provides for a business transaction combination pursuant to which, among other things and in accordance with the terms and subject to the conditions of the merger agreement, Let’s Go will merge with and into Rimini Street, with Rimini Street as the surviving corporation (which we refer to as the first merger). The surviving corporation from the first merger will then merge with and into GPIA, with GPIA as the surviving corporation (which we refer to as the second merger). Prior to and as a condition of the mergers, GPIA will change its jurisdiction of incorporation by effecting a deregistration under Article 206 of the Cayman Islands Companies Law and a domestication under Section 388 of the DGCL, pursuant to which GPIA’s jurisdiction of incorporation will be changed from the Cayman Islands to the State of Delaware. The mergers will follow the domestication.

The aggregate merger consideration is $775 million, subject to certain adjustments identified in the merger agreement, and is payable entirely in newly issued common stock of RMNI based on a per share issue price of $10.00 per share.

After consideration of the factors identified and discussed in the section entitled “ Rimini Street Business Combination Proposal—Rimini Street’s Board of Directors’ Reasons for the Business Combination ”, Rimini Street’s board of directors concluded that the business combination, on the terms and conditions set forth in the merger agreement and other related documents, is advisable and fair to, and in the best interests of, Rimini Street’s stockholders.

For additional information, see the section entitled “ Rimini Street Business Combination Proposal ” in this joint proxy statement/prospectus.

Rimini Street Preferred Stock Conversion Proposal

Pursuant to the merger agreement, the holders of Rimini Street common stock will be entitled to the right to receive the applicable portion of merger consideration. As a result, in order to participate in the merger consideration provided to the holders of Rimini Street common stock, the holders of Rimini Street preferred stock are requesting the automatic conversion of all outstanding shares of Rimini Street preferred stock into shares of Rimini Street common stock.

For additional information, see the section entitled “ Rimini Street Preferred Stock Conversion Proposal ” in this joint proxy statement/prospectus.

Date, Time and Place of Special Meeting of Rimini Street’s Stockholders

The special meeting of the stockholders of Rimini Street will be held at [•] [a.m.][p.m.], Pacific Time, on [•], 2017, at [•], to consider and vote upon the proposals to be put to the special meeting.

Voting Power; Record Date of Special Meeting of Rimini Street’s Stockholders

Rimini Street stockholders will be entitled to vote or direct votes to be cast at the special meeting if they owned shares of Rimini Street capital stock at the close of business on [•], 2017, which is the record date for the special meeting. Each share of Rimini Street Class A Common Stock is entitled to one vote per share at the special meeting and each share of Rimini Street Class B Common Stock is entitled to fifteen votes per share at the special meeting. Each share of Rimini Street Series A Preferred Stock, Series B Preferred Stock and Series C Preferred Stock is entitled to the number of votes equal to the number of shares of Class A Common Stock or Class B Common Stock, as applicable, into which the shares of preferred stock held by such holder could be converted as of the record date. As of the record date, each share of Rimini Street Series A Preferred Stock and Rimini Street Series B Preferred Stock will convert into one share of Rimini Street Class B Common Stock and each share of Rimini Street Series C Preferred Stock will convert into one share of Rimini Street Class A Common Stock. As of the close of business on the record date, there were [•] shares of Rimini Street Class A Common Stock, [•] shares of Rimini Street Class B Common Stock, [•] shares of Rimini Street Series A Preferred Stock, [•] shares of Rimini Street Series B Preferred Stock, and [•] shares of Rimini Street Series C Preferred Stock outstanding and entitled to vote.

Quorum and Vote of Rimini Street Stockholders

A quorum of Rimini Street stockholders is necessary to hold a valid meeting. The presence, in person or by proxy, of a majority of the aggregate voting power of the capital stock issued and outstanding and entitled to vote constitutes a quorum at the special meeting. Abstentions, while considered present for the purposes of establishing a quorum, will not count as votes cast at the special meeting.

As of the record date for the special meeting, [•] shares of Rimini Street capital stock would be required to achieve a quorum.

The proposals presented at the special meeting require the following votes:

converted as of the record date), and (iii) the majority of the outstanding shares of Rimini Street Class A Common Stock and Rimini Street Class B Common Stock, voting as a single class, present in person or represented by proxy at the Rimini Street special meeting is required to approve the Rimini Street business combination proposal.

Abstentions, while considered present for the purposes of establishing a quorum, will not count as votes cast at the special meeting.

Appraisal Rights for Rimini Street Stockholders

Rimini Street stockholders will be entitled to dissenters’ rights only if they comply with the Nevada law procedures summarized in the section entitled “ Appraisal Rights ”. To be eligible to exercise appraisal rights, record holders of Rimini Street capital stock must not vote in favor of the business combination and must properly demand payment for their shares. The entirety of sections 92A.300 to 92A.500 of the Nevada Revised Statutes (the “Nevada Dissenter’s Rights Statute”) is provided on Annex I to this joint proxy statement/prospectus. Upon effectiveness of the business combination, any Rimini Street stockholder who has perfected its dissenters’ rights and who believes that the merger consideration is insufficient will have the right to object and have a court in Nevada determine the value of each share of stock, and to be paid the appraised value determined by the court, which could be more or less than the merger consideration.

Proxy Solicitation for Rimini Street

Proxies may be solicited by mail, telephone or in person.

If a stockholder grants a proxy, it may still vote its shares in person if it revokes its proxy before the special meeting. A shareholder also may change its vote by submitting a later-dated proxy as described in the section entitled “ Special Meeting of Rimini Street Stockholders—Revoking Your Proxy ”.

Interests of Rimini Street’s Directors and Officers in the Business Combination

When you consider the recommendation of Rimini Street’s board of directors in favor of approval of the Rimini Street business combination proposal, you should keep in mind that Rimini Street’s directors and officers have interests in such proposal that are different from, or in addition to, those of Rimini Street stockholders generally. These interests include, among other things, the interests listed below:

The existence of financial and personal interests of one or more Rimini Street directors may result in a conflict of interest on the part of such director(s) between what he, she or they may believe is best for Rimini Street. See the sections entitled “ Risk Factors ” and “ Rimini Street Business Combination Proposal—Interests of Rimini Street’s Directors and Officers in the Business Combination ” for a further discussion of this and other risks.

Recommendation to Stockholders of Rimini Street

Rimini Street’s board of directors believes that the Rimini Street business combination proposal and the Rimini Street preferred stock conversion proposal are in the best interest of Rimini Street’s stockholders and recommends that its stockholders vote “FOR” the Rimini Street business combination proposal and “FOR” the Rimini Street preferred stock conversion proposal.

The existence of financial and personal interests of one or more of Rimini Street’s directors may result in a conflict of interest on the part of such director(s) between what he, she or they may believe is in the best interests of Rimini Street and its stockholders and what he, she or they may believe is best for himself, herself or themselves in determining to recommend that stockholders vote for the proposals. See the section entitled “ Rimini Street Business Combination Proposal—Interests of Rimini Street’s Directors and Officers in the Business Combination ” in the accompanying joint proxy statement/prospectus for a further discussion of this.

Conditions to the Closing of the First Merger

Unless waived by the parties to the merger agreement, and subject to applicable law, the consummation of the first merger is subject to a number of conditions set forth in the merger agreement including, among others, receipt of the requisite shareholder approvals contemplated by this joint proxy statement/prospectus. For more information about conditions to the consummation of the first merger, see “ GPIA Business Combination Proposal—The Merger Agreement—Conditions to Closing of the First Merger ”.

Sources and Uses of Funds for the Business Combination

It is currently expected that the business combination will be consummated by August 31, 2017. The following table summarizes the sources and uses for funding the business combination assuming consummation of the business combination as of May 31, 2017 (being the most recent date for which Rimini Street month end balance sheet data is available) and August 31, 2017, respectively, and assuming that (i) RMNI issues the number of shares of RMNI common stock to the former equityholders of Rimini Street pursuant to the merger agreement as specified in the table below, (ii) the Sponsor does not subscribe for any common shares pursuant to its equity commitment at or prior to the consummation of the business combination, and (iii) no public shareholders exercise their redemption rights in connection with the business combination. Where actual amounts are not known or knowable, the figures below represent GPIA’s good faith estimate of such amounts assuming a closing as of May 31, 2017 (being the most recent date for which Rimini Street month end balance sheet data is available) and August 31, 2017, respectively.

unrestricted net cash and cash equivalents of GPIA on the date that the mergers are consummated, will be accounted for as a capital infusion into Rimini Street whereby all of the expenses incurred by Rimini Street related to the business combination will be charged to additional paid-in capital upon consummation of the mergers.

Comparison of Corporate Governance and Shareholder Rights

The domestication will change GPIA’s jurisdiction of incorporation from the Cayman Islands to Delaware, and as a result, GPIA’s organizational documents will change and will be governed by the DGCL rather than Cayman Islands Companies Law. There are differences between Cayman Islands corporate law, which currently governs GPIA, and Delaware corporate law, which will govern RMNI following the domestication. Additionally, there are differences between the new organizational documents of Rimini Street, Inc. and the current constitutional documents of GPIA.

For a summary of the material differences among the rights of holders of RMNI common stock and holders of GPIA ordinary shares, see “ Comparison of Corporate Governance and Shareholder Rights ”.

Regulatory Matters

The business combination and the transactions contemplated by the merger agreement are not subject to any additional federal or state regulatory requirements or approvals, except for (i) required filings under the Hart-Scott-Rodino Antitrust Improvements Act of 1976 (the “HSR Act”) and (ii) filings with the Cayman Islands, the State of Delaware and the State of Nevada necessary to effectuate the transactions contemplated by the merger agreement. On June 2, 2017, Rimini Street and GPIA made the filings required to be made under the HSR Act. On June 28, 2017, the U.S. Federal Trade Commission (the “FTC”) notified Rimini Street that early termination of the waiting period under the HSR Act was granted, effective immediately. Therefore, the closing condition of the merger agreement relating to the expiration or termination of the applicable waiting period under the HSR Act has been satisfied.