Diagnosis
You want to create a document of document type &V1& and assign thedocument number externally.
Via settings in Customizing (Document management), it is defined thatdocument numbers are only assigned internally by the system fordocument type &V1&.

Procedure

• Remove your entry for the document number by entering "!" at the
beginning of the field.

• When you save the document, you see a message telling you which
document number was created.