What is KSeF? Poland's national e-invoicing system explained

KSeF (Krajowy System e-Faktur — the National e-Invoice System) is Poland's central platform for structured invoices, run by the Ministry of Finance. Unlike Peppol, which is a decentralised network of Access Points, KSeF is a single government hub: you issue an invoice into KSeF, and your buyer retrieves it from KSeF.

How KSeF works

1. You create a structured invoice in the FA_VAT XML format.
2. Your software sends it to KSeF (via its API), authenticated.
3. KSeF validates it, assigns a unique KSeF number, and returns an official

confirmation — the UPO (Urzędowe Poświadczenie Odbioru).

1. The invoice is considered issued at the moment KSeF accepts it.
2. Your buyer accesses it directly in KSeF.

There's no "send to the customer" step in the Peppol sense — KSeF is the delivery channel for domestic invoices.

The FA_VAT format

Invoices must follow the Ministry's structured schema (FA(2), with FA(3) introduced as the system evolves). It's a defined XML — not a PDF. A PDF can exist as a human-readable visualisation, but the legal invoice is the structured file in KSeF.

The KSeF number and UPO

• KSeF number — the unique ID KSeF assigns; it identifies the invoice

officially.

• UPO — your proof the invoice was received and accepted. Keep it; it's the

equivalent of a delivery receipt.

Who must use it, and when

KSeF becomes mandatory on a phased calendar (after an earlier postponement): larger taxpayers first, then the rest of businesses. Exact dates have shifted before, so confirm your phase with a Polish tax advisor — but the direction is fixed: structured invoicing through KSeF for domestic trade.

Authentication

You identify to KSeF with a qualified electronic signature or seal, a trusted profile, or a token generated inside KSeF for your software. See KSeF integration.

KSeF vs Peppol

• KSeF — Poland's domestic national system; centralised; FA_VAT.
• Peppol — the EU cross-border network; decentralised; UBL/EN 16931.

A Polish business that also trades across the EU deals with both worlds.

Where Eurobillr fits

Eurobillr focuses on Peppol and EU e-invoicing — Belgium, France (via an accredited platform), Italy SDI, Germany XRechnung — so if you invoice across borders from or into Poland, Eurobillr covers the EU/Peppol side. KSeF itself is Poland's domestic system; for domestic Polish issuance you use a KSeF-connected solution. If KSeF matters to your setup, tell us — it helps us prioritise.

Next in this series: KSeF integration · how to issue a KSeF invoice.