German E-Invoice Validation Must Cover XML, Business Rules and the PDF/A-3 Container

• XRechnung is a structured XML invoice, while ZUGFeRD or Factur-X combines a human-readable PDF/A-3 document with embedded structured XML. The two formats therefore require different but overlapping validation controls.  [zugferd.org], [gpdf.com]
• XML schema validation alone may not identify every business-rule, arithmetic, profile or PDF-container problem. ZUGFeRD validation should consider both the embedded XML and the integrity of the PDF/A-3 carrier. [rechnex.de], [zugferd.org], [mustangserver.de]
• Validation reports, tool versions, warnings and errors should be retained with the invoice audit trail. This evidence can help explain why a document was accepted internally but rejected by a customer or portal.

Extended article

German electronic-invoice validation should reflect the actual format being exchanged.

XRechnung is an XML-based format. ZUGFeRD or Factur-X is a hybrid document consisting of a PDF/A-3 file containing embedded machine-readable XML. Validating only a separately extracted XML file does not necessarily establish that the final hybrid invoice is fully compliant. [zugferd.org], [gpdf.com]

For XRechnung, validation ordinarily involves the relevant XML schema, EN 16931 rules, German CIUS requirements and applicable Schematron business rules.

For ZUGFeRD, the process must additionally address whether the PDF complies with the relevant PDF/A requirements, whether the XML is properly embedded, whether the correct profile is used and whether the visible PDF and machine-readable data represent the same invoice.

Mustang can validate several ZUGFeRD, Factur-X and XRechnung formats and produces an XML report. The ZUGFeRD tools overview also identifies veraPDF for PDF/A validation and describes Mustang as a tool for extracting, combining and validating ZUGFeRD or Factur-X content. [zugferd.org], [mustangserver.de]

A controlled validation process should preserve the invoice, the validation result, the ruleset or profile applied and the tool version. Businesses should also decide how warnings are treated rather than retaining only fatal errors.

External sources: ZUGFeRD open-source tools and validators, Mustang validation service and supported formats and overview of combined KoSIT, Mustang and veraPDF validation. [zugferd.org], [mustangserver.de], [rechnex.de]