Validation rules

UBL-SR-39

The project reference (BT-11) appears more than once — only one cac:ProjectReference with one cbc:ID is allowed.

Rule: UBL-SR-39 — official EN 16931 / XRechnung rule
Severity: error
Detected by: tier 3 — KoSIT validator (authoritative)
Reachability: Only reachable when validating your own XML — normbill-generated documents cannot trigger it

The normbill invoice model has no project reference; generated XML never contains cac:ProjectReference.

How to fix it

Keep a single ProjectReference element in your XML.

UBL-SR-39 auf Deutsch — was bedeutet der Fehler?

Der KoSIT-Validator lehnt die Rechnung ab, weil die Projektreferenz (BT-11) mehrfach vorkommt — nur ein cac:ProjectReference mit einer cbc:ID ist erlaubt.

So beheben Sie den Fehler

Behalten Sie genau ein ProjectReference-Element im XML.

Official sources

Every 422 from the API lists the rule id, the path in your request JSON, a plain-language message and a suggested fix — see the docs overview for the report format.

Or try it live: drop any XRechnung XML on the free validator — same KoSIT-backed report, no account.