TP Flexible Income Fund 10-K 2022 FY Annual report

Exhibit 32.1

CERTIFICATION BY CHIEF EXECUTIVE OFFICER

CERTIFICATION PURSUANT TO

18 U.S.C. SECTION 1350,

AS ADOPTED PURSUANT TO

SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

In connection with the Annual Report on Form 10-K of Prospect Sustainable Income Fund, Inc. (the “Company”) for the period ended June 30, 2022, as filed with the Securities and Exchange Commission on the date hereof (the “Report”), I, M. Grier Eliasek, Chief Executive Officer of the Company, certify, pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that to the best of my knowledge:

1.The Report fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934, as amended; and

2.The information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company as of the dates and for the periods expressed in the Report.

/s/ M. Grier Eliasek

    M. Grier Eliasek

    Chief Executive Officer

    (Principal Executive Officer)

    Date: September 6, 2022