There are a lot terms and standards around electronic invoices:
- ZUGFeRD was developed by a German initiative as a standard for electronic invoices (https://www.ferd-net.de/).
- ZUGFeRD 2.1 is identical to the German/ French cooperation Factur-X (ZUGFeRD 2.1 = Factur-X 1.0) (https://www.ferd-net.de/standards/what-is-factur-x/index.html).
- The standard Factur-X 1.0 (respectively ZUGFeRD 2.1) is conform with the European norm EN 16931.
- EN 16931 in turn is based on worldwide UN/CEFACT standard ‘Cross Industry Invoice’ (CII).
- XRechnung as another German standard is a subset of EN 16931. It is defined by another party called KoSIT (https://www.xoev.de/). It comes with its own validation rules (https://www.ferd-net.de/standards/what-is-xrechnung/index.html).
This means that both Factur-X 1.0 (respectively ZUGFeRD 2.1) and XRechnung are conform with EN 16931. This does not automatically result that those invoices are per se identical - To achieve compatibility, ZUGFeRD 2.1.1 introduced a XRechnung reference profile to guarantee compatibility between the two sister formats.