Reason code for short payment received from Customers

Hello

We are on ECC 6.0 without application of any enhancement package.

Requirement is to capture reasons of short payment received from customer and generate a report based on such reason codes.

Reasons of short payment received could be - Adhoc payment; Excess billed; Tax deducted at source (TDS) on freight / service charges and Bank charges etc.

Let me know relevant configuration required.

Would reason codes be captured during incoming payment entry or customer account clearing?

Thanks.

Vimal, India