By including a per diem amount in the letter, the parties will not have to execute another payoff letter if the termination date. A 10 day payoff is crucial to getting your old loans paid off during a refinance.Learn how it works from start to finish. Complete and submit a payoff worksheet at least 30 days prior to the anticipated payoff date. Include a completed Request for Action (RFA) form. It typically details the principal balance, interest due as of that date, per diem, any late fees, etc. Please include a per diem amount in the statement. Please email this information to as soon as possible. NOTE: the payoff amount listed is only valid for that day. By setting up Auto Pay in MyAccount online or on the GM Financial Mobile app, you can have your payments automatically withdrawn from your bank account.