Reference Number - Lockbox

Dear SAP Gurus,

While entering the invoice for customer in t.code FB70 and maintaining the reference number as an invoice number. In Lockbox file the reference number is the invoice number.

But when importing the lockbox file with FLB2 system is showing the error <u>document not found</u>. Actually it is looking for the document number in the Lockbox file. But my company wants the system to go with the reference number. So how can we make it possible.

Thanks & Regards,

Sim