E-Invoice Compliance

The Payment Gateway implements robust native e-invoicing pipelines capable of satisfying B2B and B2G (Business to Government) mandates globally. It generates legally compliant machine-readable XML structures embedded within PDF/A-3 archives or delivered standalone.

Core Mandates & Validation

The system's invoice generation is actively verified against official EU schemas (EN16931).

The supported standards currently include:

1. ZUGFeRD / Factur-X: A hybrid XML/PDF format dominant in Germany and France.
2. Peppol BIS Billing 3.0: An international standard mapped back to UBL (Universal Business Language).
3. XRechnung: A strict UBL subset essential for German B2G transactions.

Validation testing is performed via strict Schematron rule mapping (e.g., FACTUR-X_EN16931.xslt, PEPPOL-EN16931-UBL.xslt) using external engines like ecosio.

The ZUGFeRD / Factur-X Generation Pipeline

Generating a ZUGFeRD document securely without destroying the underlying Chromium/Gotenberg PDF rendering layer is highly complex.

1. PDF Generation: A high-fidelity base invoice PDF is rendered using Gotenberg (HTML to PDF).
2. CII Conversion: The platform transforms its internal model (portal invoice) into the Factur-X Cross Industry Invoice (CII) schema.
3. Incremental PDF Update: Rather than risking destructive full rewrites using third-party PDF libraries, the gateway safely appends the required artifacts using an incremental update.
4. Zlib XML Compression: The raw CII XML stream (factur-x.xml) is explicitly compressed using compress/zlib and injected into the PDF stream using the FlateDecode filter to prevent extraction and parsing issues seen in raw deflate streams.
5. Metadata Assignment: Crucial Factur-X XMP packets and AFRelationship (Alternative File) metadata are embedded in the PDF catalog headers.

EN16931 Rules Handling

Native generation automatically enforces major business rules prescribed by EN16931 to ensure validity:

• BR-CO-25 (Missing Due Dates): If an invoice's total due is strictly positive but lacks payment terms or a due date, the system injects the default descriptive tag "Payable upon receipt".
• Empty Delivery Nodes: Extraneous XML elements, such as ApplicableHeaderTradeDelivery, are explicitly pruned when a transaction is purely virtual/digital.
• BR-FX-EN-04: Non-down-payment invoices lack structured delivery times. The system safely falls back to recording the delivery event date as the UTC IssueDate.

Effective Provider Strategy

As different regions require varying formats (or restrict them entirely), the API strictly resolves the correct format using a dual-layered hierarchy:

1. Organization-Level Rules: Configures what the organization is physically capable of generating globally via settings.invoicing.eInvoice.allowedFormats.
2. Portal-Level Exposure: Determines which of those generated formats should be visibly offered to the end-consumer via the customer portal (settings.portal.allowedDownloadFormats).

The resulting configuration dictates whether /portal/documents/:id/einvoice should yield a UBL XML stream, a hybrid ZUGFeRD PDF, or simply standard static binary PDF representations.