Sec Form 4 Filing - South Mountain LLC @ BTRS Holdings Inc. - 2021-01-12

FORM 4 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 South Mountain LLC 2. Issuer Name and Ticker or Trading Symbol BTRS Holdings Inc. [ SMMC] 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) C/O SOUTH MOUNTAIN MERGER CORP., 767 FIFTH AVENUE, 9TH FLOOR 3. Date of Earliest Transaction (MM/DD/YY) 01/12/2021 (Street) NEW YORK, NY10153 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 A Common Stock 01/12/2021 M 5,000,000 ( 3 ) ( 4 ) ( 5 ) A 5,000,000 ( 3 ) ( 4 ) ( 5 ) I See footnote ( 7 ) Class A Common Stock 01/12/2021 M 500,000 A 500,000 ( 3 ) ( 4 ) ( 5 ) I See footnote ( 7 )

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 Class B Common Stock ( 1 ) ( 2 ) 01/12/2021 D( 1 )( 3 )( 4 )( 5 ) 1,250,000 ( 1 ) ( 1 ) Class A Common Stock ( 1 ) ( 3 ) ( 4 ) ( 5 ) ( 3 ) ( 4 ) ( 5 ) 5,000,000 I See footnote ( 7 ) Class B Common Stock ( 1 ) ( 2 ) 01/12/2021 M( 1 )( 2 )( 3 )( 4 )( 5 ) 5,000,000 ( 1 ) ( 1 ) Class A Common Stock ( 1 ) ( 3 ) ( 4 ) ( 5 ) ( 3 ) ( 4 ) ( 5 ) 0 I See footnote ( 7 ) Private Placement Warrants $ 11.5 01/12/2021 D( 1 ) 4,166,667 ( 3 ) ( 4 ) ( 5 ) ( 6 ) ( 6 ) Class A Common Stock ( 3 ) ( 4 ) ( 5 ) ( 3 ) ( 4 ) ( 5 ) 2,787,833 ( 3 ) ( 4 ) ( 5 ) I See footnote ( 7 ) Private Placement Warrants $ 11.5 01/12/2021 M( 3 )( 4 )( 5 ) 2,787,833 ( 3 ) ( 4 ) ( 5 ) ( 6 ) ( 6 ) Class A Common Stock 500,000 ( 3 ) ( 4 ) ( 5 ) ( 3 ) ( 4 ) ( 5 ) 0 I See footnote ( 7 )

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other South Mountain LLC C/O SOUTH MOUNTAIN MERGER CORP. 767 FIFTH AVENUE, 9TH FLOOR NEW YORK, NY10153 X Harbour Reach Holdings LLC C/O SOUTH MOUNTAIN MERGER CORP. 767 FIFTH AVENUE, 9TH FLOOR NEW YORK, NY10153 X Netherton Investments Ltd C/O SOUTH MOUNTAIN MERGER CORP. 767 FIFTH AVENUE, 9TH FLOOR NEW YORK, NY10153 X Netherton Holdings Ltd C/O SOUTH MOUNTAIN MERGER CORP. 767 FIFTH AVENUE, 9TH FLOOR NEW YORK, NY10153 X Platt Michael Edward C/O SOUTH MOUNTAIN MERGER CORP. 767 FIFTH AVENUE, 9TH FLOOR NEW YORK, NY10153 X Signatures See Signatures included in Exhibit 99.1 01/14/2021 Signature of Reporting Person Date

Explanation of Responses:

( 1 )As described in the registration statement on Form S-1 (File No. 333-231881) of South Mountain Merger Corp. ("South Mountain") under the heading "Description of Securities-Founder Shares," the shares of Class B common stock of South Mountain (the "Class B Common Stock") automatically convert into shares of Class A common stock of South Mountain (the "Class A Common Stock") at the time of South Mountain's initial business combination or earlier at the option of the holder, in each case, on a one-for-one basis, subject to adjustment for stock splits, stock dividends, reorganizations, recapitalizations and the like, and certain anti-dilution rights. ( 2 )On January 12, 2021, South Mountain consummated its initial business combination (the "Business Combination") with Factor Systems, Inc. (d/b/a Billtrust) ("Billtrust"). ( 3 )In connection with the consummation of the Business Combination (the "Closing"), (i) South Mountain LLC (the "Sponsor") forfeited 4,166,667 outstanding warrants to purchase shares of Class A Common Stock of South Mountain sold in a private placement to our Sponsor that occurred simultaneously with the completion of the IPO (the "Private Placement Warrants") and an additional 2,787,833 outstanding Private Placement Warrants were transferred by the Sponsor to South Mountain in exchange for 500,000 newly issued shares of South Mountain Class A Common Stock (the "Warrant Shares"), (ii) the Sponsor forfeited 1,250,000 outstanding shares of South Mountain Class B Common Stock, par value $0.0001 per share, to South Mountain for no consideration, and (iii) the 5,000,000 remaining shares of South Mountain Class B Common Stock held by the Sponsor not otherwise forfeited, converted to South Mountain Class A Common Stock. An aggregate of 3,125,000 of the shares of South Mountain (con't on FN 4) ( 4 )(con't from FN 3) Class A Common Stock vested immediately following Closing. The 500,000 Warrant Shares and remaining 1,875,000 shares of South Mountain Class A Common Stock will each vest in two equal tranches if the stock price level is greater than or equal to $12.50 per share (the "$12.50 Share Price Milestone") or $15.00 per share (the "$15.00 Share Price Milestone"), in each case over 20 of 30 trading days within five years of Closing, subject to equitable adjustment to reflect any subdivision, stock split, stock dividend, reorganization, combination, recapitalization or similar transaction with respect to the South Mountain Common Stock. In addition, the shares subject to the $12.50 Share Price Milestone or the $15.00 Share Price Milestone will accelerate vesting upon certain acceleration events, including a change of control of in which the value of the consideration to be received by holders of the common stock of the surviving (con't on FN 5) ( 5 )(con't from FN 4) corporation in such change of control event is at least $12.50 per share, or $15.00 per share, respectively. Any shares subject to vesting pursuant to the Share and Warrant Cancellation Agreement, dated as of October 18, 2020, among the Sponsor, the Company and Billtrust will be forfeited to the extent such shares remain unvested following the five year anniversary of the Closing. ( 6 )The Private Placement Warrants were purchased by the Sponsor on June 19, 2019. Each Private Placemen t Warrant is exercisable for one Class A Share at an exercise price of $11.50 per Class A Common Stock, subject to certain adjustments. The Private Placement Warrants may be exercised only during the period commencing 30 days after the first date on which South Mountain completes a business combination and expires five years after the completion of South Mountain's business combination or earlier upon redemption or liquidation. ( 7 )South Mountain LLC is the sponsor entity of South Mountain. The managing member of the Sponsor is Harbour Reach Holdings LLC, whose managing member is Netherton Investments Limited, whose sole shareholder is Netherton Holdings Limited, whose sole shareholder is Mr. Michael Platt.

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