The formats
All European mandates accept formats conforming to EN 16931, the European core invoice standard.
UBL 2.1 Invoice
Universal Business Language, the XML vocabulary under almost every European e-invoice format.
Peppol BIS Billing 3.0
The Peppol network's billing profile built on UBL 2.1 and EN 16931.
XRechnung 3.0
Germany's national implementation (CIUS) of EN 16931, mandatory for German public-sector buyers since 2020 and the standard format for German B2B e-invoicing.
Factur-X / ZUGFeRD 2.x
A hybrid: a normal human-readable PDF (PDF/A-3) with the legally relevant XML embedded inside it.
KSeF FA(3) (Poland)
Poland's national structured-invoice schema, built and operated by the Ministry of Finance.
EN 16931 in one paragraph
The European standard defines a core model of invoice fields (numbered BT-1 to BT-155, plus business groups BG-2 to BG-30) that every compliant format must carry. A "profile" is a country's or network's restriction of that model. If your invoice validates against one profile, the data model is the same everywhere: what changes is the serialization (UBL XML, CII XML, or PDF-embedded) and a handful of national fields.