By including a per diem amount in the letter, the parties will not have to execute another payoff letter if the termination date. A payoff agreement is an informal contract in which a creditor agrees to accept the balance of a debt owed as full payment.A 10 day payoff is crucial to getting your old loans paid off during a refinance. Learn how it works from start to finish. And receiving reimbursement for your actual per diem costs up to the locality rate for the OCONUS location. Is it possible to refinance my contract?