Background Checks: Sf85p - Self Employment

For a verifier to self employment what form does OPM sends them? Is it INV 41 form? But INV 41 form is to check employment and some of the questions on the form will be confusing to a verifier of self employment. Does anybody on this forum gave reference as verifier? If so please help me as I am very confused. My verifier for self employment is not my employer. I just did some software testing work for my friend while I am self employed. So he will be my verifier but not my employer or supervisor. Please help me

Background Checks: Sf85p - Self Employment