E-Invoice API
Convert, validate and calculate e-invoices over a single REST endpoint.
A REST API over Mustang for working with European e-invoice formats — Factur-X, ZUGFeRD, XRechnung (CII) and Order-X.
You can convert an invoice XML into a PDF/A-3 hybrid, pull the XML back out of one, validate a document against the format rules, or calculate the totals for an invoice that does not have them yet.
Start here
Getting started
Your first call, from key to response.
Authentication
How to send your API key, and what the errors mean.
Sandbox and live
One URL, two environments, chosen by which key you send.
Errors
Gateway errors and Mustang's own error format.
The whole thing in one call
curl https://staging-api-e-invoice.officefreund.de/api/v1.8.2/e-invoice/ping \
-H "Authorization: Bearer of_test_your_key_here"
# pongThat is a sandbox key, so nothing was spent against your production allowance
and the call was rate-limited harder than a live one. The document processing
itself is real — the sandbox runs the same Mustang engine. Swap of_test_ for
of_live_ and the same URL bills against your quota instead.
The machine-readable spec
The full OpenAPI document is at
/openapi.yaml. Point a generator at it directly:
npx openapi-typescript https://staging-docs-e-invoice.officefreund.de/openapi.yaml -o api.d.ts