Diagnosis
A material number is specified in the transferred item (SAP materialnumber as it is used in YOUR system; not a customer material number),that is not available in the determined sales document/ in thedetermined delivery.

System Response
The item cannot be processed in this way.

Procedure
You can change the transferred material number using the "ProcessErrors" function.
In this case, however, you must first ensure that the data is correct inthe subsequent successful assignment of transferred item to an item inthe sales document/in the delivery.
You must check in any case why there is a discrepancy in the materialnumber. It is possible that your customer is using an incorrect materialnumber that is then transferred incorrectly into the self-billingprocess.
Contact your customer in order to agree on the number.