Poland Releases Final Version of FA(3) Schema and KSeF 2.0 API Documentation
In preparation for the mandatory implementation of the National e-Invoicing System (KSeF) starting February 1, 2026, the Polish Ministry of Finance has released final versions of key technical components of the system. These include the target logical structure of the FA(3) e-invoice, the complete KSeF 2.0 API documentation, and extended support materials for system integrators and users.
Final Version of the FA(3) Structure
As previously announced, the Polish Ministry of Finance has published the final version of the FA(3) logical structure for structured e-invoices. This new schema will replace the current FA(2) version as of February 1, 2026.
The new structure has been developed based on the outcomes of tax consultations and input provided by entrepreneurs, accountants, auditors, and IT sector representatives. It introduces several important changes, including new VAT rate codes and the ability to attach supplementary files to invoices.
The release is accompanied by detailed documentation, an informational brochure, and sample invoice files. All materials are available in the Central Repository of Electronic Document Templates (ePUAP).
Complete API Documentation for KSeF 2.0
Alongside the new schema, the Ministry has published detailed documentation for the KSeF 2.0 API to support integrators of invoicing systems in preparing for implementation within a test environment.
The published materials include:
- API specification in OpenAPI 3.0.4 format – serving as the core integration contract, fully compatible with documentation, testing, and code generation tools;
- Interactive online documentation – presenting all endpoints, parameters, data schemas, response codes, and sample calls;
- KSeF 2.0 Integration Guide – covering detailed API usage scenarios such as authentication, invoice submission in interactive and batch modes, and receipt (UPO) retrieval, with examples in C# and Java;
- Overview of key changes in KSeF 2.0 API – summarizing the main improvements over previous versions;
- .NET and Java integration libraries – including ready-to-use components for implementing the KSeF 2.0 client and demo applications.
This documentation enables integrators to begin architectural planning and prototype development ahead of the test environment launch.
KSeF 2.0 Rollout Timeline
- September 30, 2025 – release of the KSeF 2.0 API test environment for integrators and businesses;
- November 2025 – planned launch of the test version of the KSeF 2.0 Taxpayer Application, featuring full API functionality;
- February 1, 2026 – production launch of the system and the start of the obligation to issue structured invoices in accordance with FA(3).
Additional Resources on KSeF 2.0
The Ministry of Finance has also prepared a set of educational and informational materials providing further clarification on:
- The legal framework for implementing KSeF,
- The scope of mandatory use,
- Operational modes of the system (offline24, partial and full outages),
- The use of QR verification codes,
- How to obtain KSeF certificates,
- The role of the KSeF number and batch identifier.
These resources are available on the Ministry of Finance’s website dedicated to KSeF.
There’s more you should know about e-invoicing in Poland – learn more about the new and upcoming regulations.
