FA_VAT is the mandatory e-invoice format for the Polish KSeF system (Krajowy System e-Faktur). Unlike formats such as NLCIUS or XRechnung, FA_VAT is not a variant of the European standard EN 16931 but an entirely separate XML schema developed by the Polish Ministry of Finance.

FA_VAT (Faktura VAT) is the XML structure that every invoice must follow to be accepted by KSeF. The schema defines all mandatory and optional fields for Polish VAT invoices, including corrective invoices and credit/debit notes.

The KSeF system operates as a pre-clearance model: each invoice is first submitted to the tax authority, validated and assigned a unique reference number before the recipient can retrieve it.

econnect-docid::http://crd.gov.pl/wzor/2025/06/25/13775::Faktura##ksef::3.0

The process consists of four steps:

1. The sender creates an invoice in FA_VAT XML (schema FA(3)).
2. The invoice is uploaded to KSeF.
3. KSeF validates the invoice and assigns a unique reference number.
4. The recipient retrieves the invoice via KSeF or through their Access Point.

The KSeF reference number serves as proof that the invoice has been registered with the tax authority and must be stored in the sender's ERP system.

Tip: an offline mode is available for situations where KSeF is temporarily unavailable. Invoices may then be created offline and must be uploaded by the next business day at the latest.

For cross-border invoices (e.g. the Netherlands to Poland), Peppol BIS Billing V3 is used, not FA_VAT.

The KSeF obligation is introduced in phases:

All VAT-registered entities in Poland must be able to receive KSeF invoices from 1 February 2026.

eConnect fully supports FA_VAT. When you send an invoice to a Polish recipient via KSeF, the PSB automatically transforms your UBL invoice into FA_VAT XML (schema FA(3)). If you already supply your invoice in FA_VAT format, it is forwarded directly. After clearance you receive the KSeF reference number back via the webhook.

• E-invoicing in Poland
• Peppol BIS Billing V3
• NLCIUS: the Dutch standard
• From semantics to syntax