Decided to start publishing very short posts about typical issues/mistakes map developers make working on the maps.
And Vendor Number is one of the things (unexperienced) developers often do not understand. For some reasons they think it is some kind of an additional document identifier, like PO number – and map it (I witnessed it multiple times) to things like Sales Order number, End Customer PO number or even PO number itself.
The reality is that Vendor Numbers are IDs buyer/purchaser assigns to its vendors/suppliers, and it stays the same across the documents with the same sender/receiver ID.
Usually it comes in Purchase Orders (X12 850) as
and should be sent back in Invoices (X12 810) the same way
In some cases it might be even hardcoded in the outbound maps.