Hi Lee,
Please refer to SAP Note 410799.
If the field NPLNR is available in structure BSIS, then simply add the field NPLNR to customer include structure CI_BSIS. This case 1 as described in the SAP Note.
If you have any additional fields (other than from structure BSIS), then BTE 00005021 should be implemented which requires custom coding. This is case 2. Here you can also find some information on how to proceed.
Best regards,
Sander
