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Compliant e-invoices in one POST request. Generate, validate and parse XRechnung and ZUGFeRD / Factur-X. Made in Germany, hosted in the EU.

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© 2026 VIBOA UG (haftungsbeschränkt) · HannoverDE · EN

Not legal or tax advice. XRechnung® is a standard of KoSIT; ZUGFeRD® of FeRD. Names used for format identification only.

DocumentationAuthenticationYour first invoiceThe 422 reportQuotas & limitsTest vs. live keys
API referencePOST…/generatePOST…/validatePOST…/parse
ReferenceError codesValidation rulesInteractive referenceOpenAPI spec↗@normbill/xrechnung↗Status

Validation rules

UBL-SR-08

The invoicing period (BG-14) appears more than once — only one document-level cac:InvoicePeriod is allowed.

Rule
UBL-SR-08 — 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 serializer emits at most one document-level InvoicePeriod, from invoice.invoicing_period.

How to fix it

Keep a single cac:InvoicePeriod at document level; per-line periods belong inside the invoice lines (BG-26).

UBL-SR-08 auf Deutsch — was bedeutet der Fehler?

Der KoSIT-Validator lehnt die Rechnung ab, weil der Abrechnungszeitraum (BG-14) mehrfach vorkommt — nur ein cac:InvoicePeriod auf Dokumentebene ist erlaubt.

So beheben Sie den Fehler

Behalten Sie genau eine cac:InvoicePeriod auf Dokumentebene; Zeiträume je Position gehören in die Rechnungsposition (BG-26).

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.