fatalEN 16931syntax binding ruleUBL
Project reference shall occur maximum once.
'Project reference' appears more than once, and this profile allows it at most once.
Keep the single correct 'Project reference' and delete the rest. Repeating an element that the semantic model treats as singular is usually a serialiser writing every value it has instead of choosing one.
UBL — context /ubl:Invoice | /cn:CreditNote
(count(cac:ProjectReference/cbc:ID) <= 1)