All our articles on format and validation: guides and news about Factur-X and the French e-invoicing reform.
The fastest way to understand what your French customer expects is to read one real file. Here is a complete EN 16931 example invoice, downloadable, walked through block by block: what each field is called in the standard, where it sits in the XML, and which checks fail when it is missing.
Create your account to send and receive over the network, and keep every file compliant.