December 18, 2020

Securities and Exchange Commission

Division of Corporation Finance

Office of Technology

100 F Street, N.E.

Washington, D.C. 20549

Attention: Edwin Kim

Re:

South Mountain Merger Corp.

Amendment No. 2 to Registration Statement on Form S-4

Filed December 14, 2020

File No. 333-249673

Ladies and Gentlemen:

On behalf of South Mountain Merger Corp. (the “Registrant”) we are writing to respond to the comments set forth in the comment letter of the staff of the Securities and Exchange Commission (the “Staff”) dated December 17, 2020 (the “Comment Letter”) relating to the above-referenced Registration Statement. The Registrant has revised the Registration Statement in response to the Staff’s comments, and, concurrently with delivery of this letter, filed with the Securities and Exchange Commission (the “Commission”) an amendment to the Registration Statement which reflects these revisions and generally updates certain information in the Registration Statement.

To assist your review, set forth below in bold is the comment of the Staff contained in the Comment Letter and immediately below such comment is the response of the Registrant with respect thereto or a statement identifying the location in the Registration Statement of the requested disclosure or revised disclosure. Please note that all references to page numbers in our responses refer to the page numbers of Amendment No. 3 (the “Amendment”) to the above-referenced Registration Statement. Capitalized terms used but not defined herein have the meanings ascribed to such terms in the Registration Statement.

Amended Registration Statement on Form S-4, filed December 14, 2020

Unaudited Historical Comparative and Pro Forma Combined Per Share Data of South Mountain and Billtrust, Page 44

Correct the Billtrust pro forma book value per share amounts to report the pro forma deficits per share.

The Registrant has revised the Registration Statement in response to the Staff’s comment. See page 44 of the Amendment.

*****

If the Staff has any questions concerning this response letter or requires further information, please do not hesitate to contact the undersigned at (212) 373-3309.

	Very truly yours,

	/s/ Raphael M. Russo

	Raphael M. Russo

cc:	Securities and Exchange Commission Joseph M. Kempf Robert Littlepage Jan Woo South Mountain Merger Corp. Charles B. Bernicker Nicholas Dermatas Factor Systems Inc. Flint Lane Mark Shifke Cooley LLP Nicole Brookshire, Esq. Matthew Browne, Esq.