Sec Form 3 Filing - BAIN CAPITAL VENTURE INVESTORS, LLC @ BTRS Holdings Inc. - 2021-01-12

FORM 3 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person BAIN CAPITAL VENTURE INVESTORS, LLC 2. Issuer Name and Ticker or Trading Symbol BTRS Holdings Inc. [ BTRS] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director X __ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) 200 CLARENDON STREET, 3. Date of Earliest Transaction (MM/DD/YY) 01/12/2021 (Street) BOSTON, MA02116 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) _____ Form filed by One Reporting Person __ X __ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Class 1 Common Stock 31,518,953 ( 1 ) ( 2 ) ( 3 ) I See footnote ( 4 )

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other BAIN CAPITAL VENTURE INVESTORS, LLC 200 CLARENDON STREET BOSTON, MA02116 X Bain Capital Venture Fund 2012, L.P. 200 CLARENDON STREET BOSTON, MA02116 X Bain Capital Venture Partners 2012, L.P. 200 CLARENDON STREET BOSTON, MA02116 X BCIP Venture Associates 200 CLARENDON STREET BOSTON, MA02116 X BCIP VENTURE ASSOCIATES-B 200 CLARENDON STREET BOSTON, MA02116 X Salem Enrique T C/O BAIN CAPITAL VENTURE INVESTORS, 200 CLARENDON STREET BOSTON, MA02116 X Agarwal Ajay C/O BAIN CAPITAL VENTURE INVESTORS, 200 CLARENDON STREET BOSTON, MA02116 X Signatures Bain Capital Venture Investors, LLC, By: /s/ Enrique T. Salem, Name: Enrique T. Salem, Title: Managing Director 01/22/2021 Signature of Reporting Person Date Bain Capital Venture Fund 2012, L.P., By: Bain Capital Venture Partners 2012, L.P., its general partner, By: Bain Capital Venture Investors, LLC, its general partner, By: /s/ Enrique T. Salem, Name: Enrique T. Salem, Title: Managing Director 01/22/2021 Signature of Reporting Person Date Bain Capital Venture Partners 2012, L.P., By: Bain Capital Venture Investors, LLC, its general partner, By: /s/ Enrique T. Salem, Name: Enrique T. Salem, Title: Managing Director 01/22/2021 Signature of Reporting Person Date BCIP Venture Associates, By: Boylston Coinvestors, LLC, its managing partner, By: /s/ Enrique T. Salem, Name: Enrique T. Salem, Title: Authorized Signatory 01/22/2021 Signature of Reporting Person Date BCIP Venture Associates-B, By: Boylston Coinvestors, LLC, its managing partner, By: /s/ Enrique T. Salem, Name: Enrique T. Salem, Title: Authorized Signatory 01/22/2021 Signature of Reporting Person Date /s/ Enrique T. Salem 01/22/2021 Signature of Reporting Person Date /s/ Ajay Agarwal 01/22/2021 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Received on January 12, 2021 (the "Effective Date") in exchange for an aggregate of 3,931,414 shares of common stock of Factor Systems, Inc. (d/b/a Billtrust), a Delaware corporation ("Former Billtrust") (the "Common Stock"), pursuant to the Business Combination Agreement, dated as of October 18, 2020, by and among South Mountain Merger Corp. ("South Mountain" and, upon consummation of the business combination, the surviving Issuer as renamed BTRS Holdings Inc.), Former Billtrust, BT Merger Sub I, Inc., a Delaware corporation and a direct, wholly owned subsidiary of South Mountain, and BT Merger Sub II, LLC, a Delaware limited liability company and a direct, wholly owned subsidiary of South Mountain (as amended by Amendment No. 1, dated as of December 13, 2020), as more particularly described in footnote (2) below. ( 2 )Included are (i) 25,752,455 shares of the Issuer's Class 1 Common Stock, par value $0.0001 per share (the "Shares"), received on the Effective Date held by Bain Capital Venture Fund 2012, L.P. ("Venture Fund 2012") in exchange for 3,562,743 shares of Common Stock; (ii) 2,515,082 Shares received on the Effective Date held by BCIP Venture Associates ("BCIP VA") in exchange for 347,951 shares of Common Stock; and (iii) 149,770 Shares received on the Effective Date held by BCIP Venture Associates-B ("BCIP VA-B" and, together with Venture Fund 2012 and BCIP VA, the "Bain Capital Venture Entities") in exchange for 20,720 shares of Common Stock. ( 3 )In addition to those shares listed in footnote (2) herein, the reporting persons may receive the following Shares: (i) 1,405,394 Shares to be received by Venture Fund 2012, 137,256 Shares to be received by BCIP VA, and 8,173 Shares to be received by BCIP VA-B, if the Issuer's closing share price equals or exceeds $12.50 for any 20 trading days within any consecutive 30-trading day period prior to January 12, 2026; and (ii) 1,405,394 Shares to be received by Venture Fund 2012, 137,256 Shares to be received by BCIP VA, and 8,173 Shares to be received by BCIP VA-B, if the Issuer's closing share price equals or exceeds $15.00 for any 20 trading days within any consecutive 30-trading day period prior to January 12, 2026. ( 4 )Bain Capital Venture Investors, LLC ("BCVI") is the general partner of Bain Capital Venture Partners 2012, L.P. ("Venture Partners 2012"), which is the general partner of Venture Fund 2012. The governance, investment strategy and decision making process with respect to the investments held by the Bain Capital Venture Entities is directed by the Executive Committee of BCVI, which consists of Enrique Salem and Ajay Agarwal. As a result, each of BCVI, Venture Partners 2012 and Messrs. Salem and Agarwal may be deemed to share voting and dispositive power with respect to all of the Shares held by the Bain Capital Venture Entities. Each of BCVI, Venture Partners 2012 and Messrs. Salem and Agarwal disclaims beneficial ownership of such securities except to the extent of its or his pecuniary interest therein.

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