An agreement letter to pay back money is a written document that outlines the terms of a financial transaction between an individual and another party. This letter is typically used when an individual needs to borrow money from someone else or repay a debt to them. It outlines the details of the repayment plan, such as how much money needs to be paid each month, as well as any additional information about the agreement, such as agreed-upon interest rates and repayment deadlines. By signing this document, both parties agree to the outlined terms and legally commit themselves to following them.