InvoiceIn
Parse and validate received e-invoices: XRechnung, ZUGFeRD, Peppol, FatturaPA, KSeF
Generate PDF, JSON & UBL invoices in 11 languages from one JSON POST.
Invovate API is a free Business API that requires apiKey authentication, is served over HTTPS and does not support CORS, so it should be called from a server.
Free REST invoice API. JSON in, PDF or JSON out. Bearer auth, 5 templates, 11 languages, no credit card. Curl, JavaScript & Python examples ready to copy.
Details from invovate.com.

Unified API suite · now live
Geocode an address, validate an email, track a flight or pull stock data with one account, one dashboard and one API key.
The Invovate API is provided by Invovate (invovate.com). Free REST invoice API. JSON in, PDF or JSON out. Bearer auth, 5 templates, 11 languages, no credit card. Curl, JavaScript & Python examples ready to copy.
Yes. The Invovate API is listed in the Business 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 Invovate API uses apiKey authentication, so you need to register for credentials before making requests.
Not directly. The Invovate API does not allow CORS, so call it from a server, serverless function or proxy instead of front-end JavaScript.
Yes. The Invovate API is served over HTTPS, so it's safe to use in production.