The e-invoice format: EN 16931, UBL and Peppol BIS Billing 3.0 in plain English
An e-invoice is not a PDF attached to an email. The law requires a structured electronic format: an XML file compliant with the European standard EN 16931, in practice in UBL syntax, delivered over the Peppol network under the Peppol BIS Billing 3.0 profile. Here is the whole technical chain explained — so that you never have to deal with it yourself.
Three layers of the format: standard, syntax, profile
| Layer | What it is | Example |
|---|---|---|
| EN 16931 (semantics) | The European standard that defines what data an invoice carries — numbers, dates, VAT rates, party identifiers (the so-called business terms, e.g. BT-1 = invoice number) | BT-1 Invoice number |
| UBL 2.1 (syntax) | The XML “language” the data is written in. The Slovak regime uses UBL; the standard also permits CII | <cbc:ID>2027001</cbc:ID> |
| Peppol BIS Billing 3.0 (profile) | The Peppol network's rules on top of EN 16931 — validation, participant identifiers and the way a document is delivered | invoice and credit note (Invoice / CreditNote) |
In practice: your accounting or invoicing software produces UBL XML compliant with EN 16931, and a certified e-invoicing provider (a “digital postman”) delivers it to the recipient through its Peppol Access Point and reports the data to the Slovak Financial Administration.
Why a PDF is not enough
A PDF invoice is a visual document made for a person. An e-invoice is a data file made for software: the recipient's system reads the line items, the totals and the VAT out of it automatically, with nothing retyped by hand. That is why, from 1 January 2027, a PDF no longer counts as an electronic invoice for domestic B2B supplies. PDFs will not disappear, though — most systems (eFaktúra included) generate a human-readable PDF alongside the XML.
What happens to EDIFACT and older formats
Companies that exchange invoices over EDIFACT today may carry on doing so — but from 1 January 2027 EDIFACT does not meet the definition of an electronic invoice for VAT purposes in domestic transactions. The data has to be converted into UBL or CII XML compliant with EN 16931; the official mapping is set out in CEN/TS 16931-3-4:2017 (the syntax binding for the UN/EDIFACT Invoice D16B). The conversion is typically handled by your IT service provider or by your certified e-invoicing provider.
Note
If you use the delivery service and the Peppol BIS format through a certified e-invoicing provider, the provider reports the data to the Slovak Financial Administration automatically.
Which documents travel through the system
- invoices (Invoice)
- credit notes and corrective invoices (CreditNote)
- self-billed invoices (self-billing) — invoices issued by the customer on the supplier's behalf; they carry a technical code of their own
- invoices for a payment received (advance payments that create a tax liability under Section 72(1))
A proforma invoice (a request for payment) does not carry the particulars of a tax document, and so it is not sent through the e-invoicing system.
How eFaktúra handles it
- we generate invoices and credit notes directly in Peppol BIS Billing 3.0 (EN 16931, UBL) — the format is never your problem
- our own production Peppol Access Point — sending and receiving are live, with no intermediaries
- UBL import, CII conversion and a Peppol XML validator for documents from other systems
- a human-readable PDF with a payment QR code is always produced alongside the XML
Frequently asked questions
Structured XML compliant with the European standard EN 16931 in UBL syntax, delivered under the Peppol BIS Billing 3.0 profile. A PDF does not meet the definition.
A profile of the Peppol network built on top of the EN 16931 standard — it adds validation rules and the way an invoice is addressed and delivered across the network. It covers both invoices and credit notes.
In your bilateral exchange, yes — but for VAT purposes on domestic supplies from 1 January 2027 EDIFACT is not an e-invoice: the data has to be converted into UBL or CII compliant with EN 16931 (CEN/TS 16931-3-4:2017).
No. The legally binding document will be the structured XML, but systems routinely generate a PDF for people alongside it — eFaktúra always does.
Sources
Sort out your e-invoicing today
Electronic invoicing becomes mandatory in 2027. Find out how to prepare and whether it applies to you.