warningEN 16931syntax binding ruleUBL
A UBL invoice should not include extensions
The document carries a UBLExtensions block.
Remove cac:UBLExtensions. EN 16931 has no semantics for extensions, so anything you put there is invisible to the receiver — if the information matters, model it with a real business term.
UBL — context /ubl:Invoice | /cn:CreditNote
not(ext:UBLExtensions)