By including a per diem amount in the letter, the parties will not have to execute another payoff letter if the termination date. What is a Payoff Agreement?A payoff agreement is an informal contract in which a creditor agrees to accept the balance of a debt owed as full payment. It typically details the principal balance, interest due as of that date, per diem, any late fees, etc. The Payoff Amount and Per Diem Amount quoted herein are effective through December 31, 2020. The Payoff Amount and Per Diem Amount quoted herein are effective through December 31, 2020. Completing and filing Form 8609 are addressed in the instructions to the form. To combat these issues, in. By setting up Auto Pay in MyAccount online or on the GM Financial Mobile app, you can have your payments automatically withdrawn from your bank account. If you're thinking about refinancing your mortgage, use this letter to get it done.