Validation rules
UBL-SR-39 — UBL rule
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.
Related rules
UBL-SR-40— The buyer trading name (BT-45) appears more than once — the customer party may carry only one PartyName/Name.UBL-SR-37— An item price discount (BT-147) appears more than once — only one cac:Price/cac:AllowanceCharge with one…UBL-SR-36— An invoice line carries more than one invoicing period (BG-26) — only one cac:InvoicePeriod per line is…UBL-SR-42— The supplier party carries more than two cac:PartyTaxScheme elements — at most two are allowed: the VAT…UBL-SR-35— An invoice line references more than one purchase order line (BT-132) — only one OrderLineReference/LineID…UBL-SR-43— A schemeID attribute is set on an AdditionalDocumentReference/cbc:ID that is not an invoiced-object…
Official sources
- XRechnung specification (KoSIT / xeinkauf.de)
- KoSIT validator on GitHub and the XRechnung validator configuration
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.