fatalEN 16931syntax binding ruleUBL
Invoice lines shall have one and only one classified tax category.
An element that EN 16931 allows at most once appears more than once: Invoice lines shall have one and only one classified tax category.
Keep the single correct occurrence and delete the rest. If you genuinely have several values, they belong in a repeatable group, not in repeated elements.
UBL — context cac:InvoiceLine | cac:CreditNoteLine
count(cac:Item/cac:ClassifiedTaxCategory) = 1