Validation rules

BR-28 — EN 16931 rule

The item gross price (BT-148) must not be negative.

Rule: BR-28 — official EN 16931 / XRechnung rule
Severity: error
Business term: BT-148 — Item gross price
Field in your JSON: invoice.lines[*].gross_price
Detected by: tier 3 — KoSIT validator (authoritative)
Reachability: Not expressible through the normbill invoice model — documented for completeness

The request schema requires gross_price >= 0 whenever it is set.

How to fix it

Use a gross price >= 0; express reductions through the price discount (BT-147), not a negative price.

BR-28 auf Deutsch — was bedeutet der Fehler?

Der Brutto-Einzelpreis (BT-148) darf nicht negativ sein.

So beheben Sie den Fehler

Verwenden Sie einen Bruttopreis >= 0; Preisnachlässe gehören in den Preisrabatt (BT-147), nicht in einen negativen Preis. Über normbill ist gross_price >= 0.

Related rules

BR-27 — The item net price (BT-146) must not be negative.
BR-29 — The invoicing period end date (BT-74) must not be earlier than its start date (BT-73).
BR-30 — An invoice line period end date (BT-135) must not be earlier than its start date (BT-134).
BR-26 — An invoice line has no item net price (BT-146).
BR-25 — An invoice line has no item name (BT-153).
BR-31 — A document-level allowance (BG-20) has no allowance amount (BT-92).

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.