
Validate EN 16931 e-invoices: XRechnung, ZUGFeRD, Factur-X, Peppol BIS.
Attestwire API is a free Data Validation API that requires apiKey authentication, is served over HTTPS and supports CORS, so it can be called from the browser.
EN 16931 validation and generation over HTTP. Errors that teach the regulation.
Details from api.attestwire.com.

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The Attestwire API is provided by Attestwire (api.attestwire.com). EN 16931 validation and generation over HTTP. Errors that teach the regulation.
Yes. The Attestwire API is listed in the Data Validation category of the public-apis directory, which only includes APIs that are free or have a free tier. Check its documentation for rate limits and paid plans.
Yes. The Attestwire API uses apiKey authentication, so you need to register for credentials before making requests.
Yes. The Attestwire API supports CORS, so front-end JavaScript can call it directly.
Yes. The Attestwire API is served over HTTPS, so it's safe to use in production.