In this configuration activity we are able to define reason codes used in payment postings. With the help of them you could have different codes and gl account postings based on different cases.
IMG Path: Financial Accounting (New) -> Accounts Receivable and Accounts Payable -> Business Transactions -> Incoming Payments -> Incoming Payments Global Settings -> Overpayment/Underpayment -> Define Reason Codes
Tables: T053R, T053S, T001
When you open the transaction you will have to choose company code for which you will be able to maintain reason codes.
On the next screen you will see a list of all defined reason codes for the particular company code. From here you could create new, copy or edit an already existing one.