A promise to pay agreement is a promissory note. It details the amount of debt outstanding, the conditions under which the money will be repaid, the interest rate, and what will happen if the money is not repaid in a timely manner.
This type of agreement is used when a customer has not paid an amount that was made available on trade credit, and the lender now insists on a formal lending arrangement to improve the odds of repayment. It may also be used with individuals, so that the seller has a preference debt that is senior to other sellers who have only extended trade credit to a person. Promise to pay agreements may be required for payday loans, car loans, and mortgages.