The e-invoice API for the 2026-2028 mandates

Quickstart

1. Get a key (20 free credits, no card):

curl -X POST https://einvoicewiz.com/v1/signup \
  -H "Content-Type: application/json" -d '{"email":"you@company.com"}'

2. Generate a validated EN 16931 invoice XML from JSON:

curl -X POST https://einvoicewiz.com/v1/generate \
  -H "X-API-Key: eiw_..." -H "Content-Type: application/json" -d '{
  "invoice_number":"RE-2026-001","issue_date":"2026-07-12","currency":"EUR",
  "seller":{"name":"Muster GmbH","line_one":"Beispielstr. 1","postcode":"10115",
            "city":"Berlin","country":"DE","vat_id":"DE123456789"},
  "buyer":{"name":"Kunde AG","line_one":"Weg 2","postcode":"60311","city":"Frankfurt","country":"DE"},
  "lines":[{"name":"Consulting","qty":2,"unit":"hour","unit_price":100.0,"vat_rate":19}]
}'

3. Or make a full Factur-X / ZUGFeRD PDF/A-3 from your existing PDF:

curl -X POST https://einvoicewiz.com/v1/facturx -H "X-API-Key: eiw_..." \
  -F "pdf=@invoice.pdf" -F 'invoice={...same JSON as above...}' -o factur-x.pdf

Endpoints

Machine-readable spec: /openapi.json (OpenAPI 3.1) · MCP server for AI agents: /mcp-server

Verification certificates

Every file that passes validation gets a permanent certificate — EIW-XXXXXXXXXXXX — returned as verify.id / verify.url in JSON responses and as X-Cert-Id / X-Verify-URL headers on binary responses. The certificate records the SHA-256 of the delivered file(s), the rule engine and version, the profile, and any warnings. Files themselves are deleted within 24 hours; the certificate is kept. A recipient (or their accountant, or an auditor) can open /verify, paste the ID or drop the file, and confirm it is the exact file that passed. This is a statement about structural conformance to EN 16931 at the time of issue — not about the commercial content of the invoice.

Failed validations are never charged — 422 responses include the exact business rules violated (BR-CO-15 etc.) so you can fix input programmatically. Totals in generated XML are always recomputed server-side from line items.

Invoice JSON reference

{
  "doc_type": 380,              // 380 invoice · 381 credit note · 384 correction
  "invoice_number": "RE-1",     // required
  "issue_date": "2026-07-12",   // required, ISO
  "due_date": null, "delivery_date": null,   // optional ISO (delivery defaults to issue)
  "currency": "EUR",            // required
  "buyer_reference": null,      // Leitweg-ID — required for XRechnung
  "order_reference": null,
  "seller": {"name","line_one","postcode","city","country","vat_id",
             "tax_number","contact_email","contact_phone","email"},   // name+country required
  "buyer":  {"name","line_one","postcode","city","country","vat_id","email"},
  "payment": {"iban","bic","terms"},
  "notes": ["..."],
  "prepaid": 0,
  "exemption_reason": null,     // for VAT categories E/AE/K/G/O
  "lines": [{"name","description","qty","unit","unit_price","vat_rate","vat_category"}]
                                // unit: piece|hour|day|kg|litre|month|km|lump|m2|m
                                // vat_category: S|Z|E|AE|K|G|O (default S, or Z when rate=0)
}

Pricing

Notes for integrators

Formats: ZUGFeRD 2.x / Factur-X 1.x (EN 16931 profile) and XRechnung 3.0 CII. Validation via the Mustang rule engine (EN 16931 BR/BR-CO, KOSIT BR-DE, PEPPOL, veraPDF-based PDF/A checks). EN 16931-1:2026 revision support is on the roadmap — breaking schema changes (CII D16B→D25A) will be versioned under /v2/ so /v1/ keeps working. Files are processed transiently and deleted immediately after the response; nothing is used for AI training (this pipeline is deterministic — no AI touches your data). GDPR DPA available on request: support@einvoicewiz.com.