A mortgage payoff letter can come in two forms. One form tells borrowers the remaining principal amount and interest they have to pay to close out the loan.Include the loan or mortgage number. 1) Primary account holder or Third Party, Please complete our Payoff Request Form and submit it to our Customer Service Department. How to fill out the Payoff Request Letter Templates? A payoff agreement is an informal contract in which a creditor agrees to accept the balance of a debt owed as full payment. Simply sign in to your online Prosper account, click the Loan Details tab, and select Download Payoff Quote. San Antonio, TX 78269-2408. Or Fax to (866) 493-1441. San Antonio, TX 78246.