Lockbox User Exit EXIT_RFEBLB20_001

Dear Experts,

For lockbox procedure in SAP customer identification is the primary task of the initial data processing of each lockbox payment. Finding the corresponding document clearing information is the second task. Lockbox program RFEBLB00 for BAI and BAI2 attempt to identify the customer first by MICR number (ABA/bank account number combination) and then by invoice number.

What could be done in the user exit if we want the system to identify the invoice number first if matches clear it and ignore the MICR number. But if invoice number is not found then go with the MICR number and post in that customer.