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Filed by a Party other than the Registrant ☐

Check the appropriate box:

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Preliminary Proxy Statement

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Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2))

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Definitive Proxy Statement

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Definitive Additional Materials

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Soliciting Material Pursuant to §240.14a-12

VERTEX, INC.

(Name of Registrant as Specified in its Charter)

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(Name of Person(s) Filing Proxy Statement, if Other Than the Registrant)

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No fee required.

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Fee paid previously with preliminary materials.

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Fee computed on table in exhibit required by Item 25(b) per Exchange Act Rules 14a-6(i)(1) and 0-11.

Signature(s) in Box Please sign exactly as your name(s) appears on Proxy. If held in joint tenancy, all persons should sign. Trustees, administra-tors, etc., should include title and authority. Corporations should provide full name of corporation and title of authorized officer signing the Proxy. Vote by Internet, Telephone or Mail 24 Hours a Day, 7 Days a Week Your phone or Internet vote authorizes the named proxies to vote your shares in the same manner as if you marked, signed and returned your proxy card. : INTERNET/MOBILE – www.proxydocs.com/verx ( PHONE – 1-866-883-3382 * MAIL – Mark, sign and date your proxy card and return it in the postage-paid envelope provided to be received no later than June 11, 2024. If you vote your proxy by Internet or by Telephone, you do NOT need to mail back your Proxy Card. Shareowner Services P.O. Box 64945 St. Paul, MN 55164-0945 The Board of Directors Recommends a Vote FOR Items 1, 2, 3 and 4. 1. Election of directors: 01 Amanda Westphal Radcliffe ■ Vote FOR ■ Vote WITHHELD 02 Stefanie Westphal Thompson all nominees from all nominees 03 Bradley Gayton (except as marked) (Instructions: To withhold authority to vote for any indicated nominee, write the number(s) of the nominee(s) in the box provided to the right.) 2. The ratification of the appointment of Crowe LLP as our independent registered public accounting firm for the fiscal year ending December 31, 2024. ■ For ■ Against ■ Abstain 3. The approval, on an advisory basis, of the compensation of our named executive officers (“Say-On-Pay”). ■ For ■ Against ■ Abstain 4. The option of “every three years” as the preferred frequency of future advisory votes on compensation of our named executive officers. ■ For ■ Against ■ Abstain THIS PROXY WHEN PROPERLY EXECUTED WILL BE VOTED AS DIRECTED OR, IF NO DIRECTION IS GIVEN, WILL BE VOTED AS THE BOARD RECOMMENDS. Address Change? Mark box, sign, and indicate changes below: ■ Date _____________________________________

2301 Renaissance Blvd King of Prussia, PA 19406 proxy This proxy is solicited by the Board of Directors for use at the Annual Meeting on June 12, 2024. The shares of stock you hold in your account or in a dividend reinvestment account will be voted as you specify on the reverse side. If no choice is specified, the proxy will be voted “FOR” Items 1, 2, 3 and 4. By signing the proxy, you revoke all prior proxies and appoint Bryan Rowland and John Schwab, and each of them with full power of substitution, to vote your shares on the matters shown on the reverse side and any other matters which may come before the Annual Meeting and all adjournments. See reverse for voting instructions. Vertex, Inc. ANNUAL MEETING OF STOCKHOLDERS June 12, 2024 9:00 a.m. EDT In order to attend the Annual Meeting, you must register at www.proxydocs.com/verx. Upon completing your registration, you will receive further instructions via email, including a unique link that will allow you access to the Annual Meeting and to vote and submit questions during the Annual Meeting. As part of the registration process, you must enter the control number located on your proxy card, voting instruction form, or Notice of Internet Availability. If you are a beneficial owner of shares registered in the name of a broker, bank or other nominee, you will also need to provide the registered name on your account and the name of your broker, bank or other nominee as part of the registration process.