CFOP not filled in document &

What causes this issue?

The CFOP was not filled in the document from which the billing document
was copied. This can be a sales or a shipping document.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Please cancel the creation of the billing document and fill the CFOP in
the originating document.

Error message extract from SAP system. Copyright SAP SE.