Reason Code for Overpayment/Underpayment in sap fico

OBBE - Define reason code for Overpayment/Underpayment
Classification of Payment Differences for underpayment and overpayment in AR line items.
With reason code, you can define whether the difference should be charged off to a G/L account or if a residual posting should be made.
A residual item results when a payment is made for less than the actual amount outstanding (1000 paid 700, outstanding 300). You clear the original open item (1000 against the customer account), and the system posts a new open item (300). This new open item is for the same amount as the original open item minus the amount paid.

OBCR - Define reason code Conversion Version

OBCS - Define Conversion of Payment Difference Reason Codes