Validation rules

BR-21

An invoice line has no line identifier (BT-126).

Rule: BR-21 — official EN 16931 / XRechnung rule
Severity: error
Business term: BT-126 — Line identifier
Field in your JSON: invoice.lines[*].id
Detected by: tier 3 — KoSIT validator (authoritative)
Reachability: Only reachable when validating your own XML — normbill-generated documents cannot trigger it

The serializer writes line.id, falling back to the 1-based line number, so generated lines always carry BT-126.

How to fix it

Give every cac:InvoiceLine a non-empty cbc:ID.

BR-21 auf Deutsch — was bedeutet der Fehler?

Eine Rechnungsposition hat keine Positionskennung (BT-126).

So beheben Sie den Fehler

Geben Sie jeder cac:InvoiceLine eine nicht-leere cbc:ID.

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.