Reference · EN 16931
Reference articles
Short pieces on the parts of European e-invoicing that are easy to get wrong. Each one
names the published documents it relies on, and says plainly what it does not cover.
The standard
UBL 2.1 and CII D16B, two syntaxes for one invoice
EN 16931 defines what an invoice means; writing it down is a separate choice of
syntax. What differs between the two, what does not, and who decides which you send.
What gets checked before an invoice is issued
The XSD gate and the Schematron gate — what each one catches, what neither can, and
why a document can be well-formed and still not be a valid invoice.
VAT categories on an invoice line
What BT-151 means, what each of the five accepted category codes is for, and which
of them oblige you to carry an exemption reason.
Correcting an invoice you have already issued
Why an issued document cannot be edited, what a credit note does instead, and how
the corrected and correcting documents stay linked.
Someone sent you an e-invoice
— what it is, how to read it, and how to check it against the EN 16931 rules.
Why a valid EN 16931 invoice can still fail a Peppol check
Peppol BIS Billing 3.0 is a usage specification of EN 16931, so it may restrict but
never relax. The specific rules a conforming invoice still fails.
EN 16931 business rules, by rule code
All 223 rules with the text the standard states them in. Look up the code from a
validation failure instead of guessing what it wanted.
EN 16931's 2026 revision, what changed and what did not
CEN published a revised standard in 2026, but the Official Journal reference and the
validation rules this site checks against still point to the 2017 edition.
The obligations
VAT in the Digital Age, the timeline and when national divergence ends
What the Council adopted in March 2025, the dates running to 2030, and why each
member state still has its own system in the meantime.
France, what applies from September 2026
Who must be able to receive and who must issue, what replaced the portail public de
facturation, and the formats the AFNOR specification defines.
Germany, XRechnung, ZUGFeRD and the 2027/2028 dates
Receiving has been obligatory since January 2025 with no relief at all. Issuing
phases in by turnover, with the format left to the parties rather than the tax
office.
KSeF, Poland's national system, and why it is not EN 16931
The February and April 2026 dates, the reliefs running to the end of 2026, and a
national schema that shares nothing with UBL or CII.
Czechia, no domestic B2B mandate, and what the B2G rule actually requires
There is no domestic B2B or B2C e-invoicing mandate in Czechia. What the B2G receiving
duty covers, and the formats it accepts.
Italy, what the SDI code (codice destinatario) actually identifies
It is not your customer's company. What the field is, and what to enter when nobody
has given you a code.