Customer payment validation

Hi FI Gurus

I have a following requirement from Indian client. Please let me know your feedback, and best practice for this requirement.

Client receives Incoming payment ( Cheque/Bank Transfer) and posts it in SAP using F-28. Cheque number or NEFT Transaction number is manually stored by user in assignment field in payment document for future reference.

Now customer wants a validation in SAP which should prevent same Cheque number / NEFT Transaction number being used more than once.

E.G. If cheque is already used to clear customer invoice(s) and user tries to post payment again with same cheque, system should give message that cheque is already applied to clear customer invoices.

Please share your experience if you have faced such scenarios before.

Through ABAP coding we can validate cheque number in assignment field, but it will be a very time consuming search.

Thanks and Regards

Kapil