Hi Curtis,
In lockbox BAI2 file, a customer is identified by MICR no. or document no.
Document no. is mentioned under Record type 4, while customer MICR no. is mentioned under record type 6.
The first step to check is if document no. is coming correctly into the BAI2 file. If yes, get the customer no. from the document and check if the customer is correctly maintained in SAP for the relevant company code.
Below is screen-shot of record type 4 which will be helpful to identify document no. from the file:
Let me know if you still face the issue.
Regards,
Gaurav