KSeF (National e-Invoicing System) has been mandatory in Poland since 1 February 2026, and since that day the only template for a structured invoice has been the FA(3) logical structure. The Ministry of Finance published its draft version on 8 May 2025 and the target version – together with the KSeF 2.0 API documentation – on 30 June 2025 (the template was added to the Central Repository of Electronic Document Templates on 25 June 2025). FA(3) replaced the previous FA(2) version and introduced a number of technical and functional changes.
The FA(3) structure has applied since 1 February 2026 and replaced FA(2). From that day, all structured invoices sent to KSeF must comply with this logical schema
Businesses and accounting offices that issue or receive invoices in KSeF already work with the new structure. The draft was released early to allow systems and accounting processes to be prepared – and for businesses that may still issue invoices outside KSeF until 31 December 2026 (invoiced sales of up to PLN 10,000 gross per month, Article 145m of the VAT Act), preparation is still relevant.
What the new FA(3) structure contains
The Ministry of Finance prepared a package of materials on the FA(3) logical structure. The published documents contain technical information and implementation guidance for different groups of KSeF users.
The package includes the XSD file defining the FA(3) structure, which is the core technical document setting out how a structured invoice is built, as well as an information brochure describing the fields and a description of the changes compared with the previous FA(2) version. The structure consists of a header, data on the parties, detailed invoice data and a footer, and a new element is a section for an invoice attachment – available to taxpayers after they notify it via the e-Tax Office (e-Urząd Skarbowy) (Article 106gba of the VAT Act).
The draft FA(3) version of May 2025 was published for consultation. The Ministry of Finance published the target version on 30 June 2025, and that is the version that has applied since 1 February 2026
Supporting materials for developers and software vendors are an important part of the documentation package. They contain practical guidance on implementing the new structure, coding examples and solutions to typical technical problems that may arise when systems are being adapted.
The technical documentation was prepared so that changes could be introduced gradually in existing accounting systems. Software vendors had time for modifications and testing – open testing of the KSeF 2.0 API started on 30 September 2025, and the pre-production (Demo) environment on 15 October 2025.
Publishing the documentation early was meant to let accounting software vendors and end users prepare for the changes. Businesses that still use the transitional exceptions also need time and a plan to move to KSeF
Implementation and application timeline
The Ministry of Finance introduced the FA(3) structure according to the timeline announced on ksef.podatki.gov.pl. The key date was 1 February 2026 – from that day FA(3) has applied and has definitively replaced the previous FA(2) version.
The period between the publication of the draft and the mandatory use of the structure was about nine months. This time was set aside for adaptation work, testing and user training.
- Publication of the draft FA(3) structure - 8 May 2025
- Publication of the FA(3) template in the Central Repository of Electronic Document Templates - 25 June 2025
- Publication of the target version of the structure and the KSeF 2.0 API documentation - 30 June 2025
- Preparation period for software vendors (API tests from 30 September 2025, Demo from 15 October 2025) - until January 2026
- Mandatory use of the FA(3) structure - from 1 February 2026
Since 1 February 2026, all structured invoices sent to the National e-Invoicing System must comply only with the FA(3) logical schema. The previous FA(2) version is no longer accepted by the system
The Ministry of Finance publishes any later changes to the template in the Central Repository of Electronic Document Templates and on ksef.podatki.gov.pl – it is worth following them, because KSeF rejects an invoice that does not match the template (Article 106nd(2)(10)(b) of the VAT Act).
Impact on businesses
The FA(3) structure directly affects everyone required to issue invoices in KSeF: from 1 February 2026, taxpayers whose sales including tax exceeded PLN 200,000,000 in 2024, and from 1 April 2026, all other taxpayers (Article 145l of the VAT Act). The changes mainly concern accounting systems, but they also affect how processes are organised within businesses.
Businesses using external accounting systems depend on whether their software vendor supports FA(3). What matters is how promptly systems are updated and how stable they are after the changes.
Businesses required to issue invoices in KSeF must use systems compatible with the FA(3) structure. An invoice that does not match the template will not be accepted by KSeF, and from 1 January 2027 failing to issue an invoice in KSeF can lead to a financial penalty (Article 106ni of the VAT Act)
Businesses with intensive trading activity and a large number of transactions need particular attention. For them, any problems with systems can seriously disrupt day-to-day operations.
Small businesses that until 31 December 2026 still use the exception for up to PLN 10,000 gross per month (Article 145m) or issue invoices from a cash register (kasa fiskalna) (Article 145n) should already agree with their software vendor how they will issue invoices in FA(3) from 1 January 2027. Planning early will help avoid problems at the end of the transitional period.
Businesses with their own IT departments can adapt their systems themselves using the published technical documentation. This, however, requires the right programming skills and a thorough understanding of the structure's specification.
| Business size | Main challenges | Recommended actions | Obligation to issue in KSeF |
|---|---|---|---|
| Micro businesses | Dependence on the software vendor | Contact the system vendor | 1 April 2026 (with invoiced sales up to PLN 10,000 gross per month - 1 January 2027) |
| Small businesses | Limited IT resources | Budget for updates | 1 April 2026 |
| Medium-sized businesses | Integration with existing systems | Review current solutions | 1 April 2026 |
| Large corporations | Complex accounting systems | Set up a project team | 1 February 2026 (sales including VAT in 2024 above PLN 200 million), otherwise 1 April 2026 |
Consequences for accounting offices
Accounting offices, which provide accounting services to a wide range of clients, faced particular challenges with the introduction of the FA(3) structure. They must ensure continuity of service for all clients – including those who still use the transitional exceptions until the end of 2026.
A key aspect is whether the accounting software in use supports FA(3) and downloading invoices from KSeF. Accounting offices often use specialised systems that need to be adapted to the specifics of their work. An office also needs access to the system — we cover this in our guide to KSeF permissions for accounting offices.
Accounting offices should check that their software supports FA(3) and downloading invoices from KSeF for all clients. Problems with the system can affect dozens or hundreds of clients at once
Integration with KSeF opens up further opportunities to automate accounting processes. Accounting offices may consider how to use the new features to streamline their work. We book clients' invoices downloaded from KSeF on an ongoing basis — this is a standard part of our bookkeeping services.
Preparing teams to work with the new structure requires appropriate training and updated internal procedures. Accounting office staff need to learn the new technical requirements and how to use the updated systems.
- Review current accounting systems for FA(3) compliance
- Contact software vendors about update schedules
- Draw up a training plan for staff using accounting systems
- Prepare procedures for testing new functions before go-live
- Communicate with clients about planned changes and their impact on cooperation
Technical aspects of the new structure
The FA(3) structure introduced a number of technical modifications compared with the previous FA(2) version. These changes concern both how information is recorded in electronic invoices and how KSeF processes them.
The XSD file defining the structure sets precise requirements for formatting data in electronic invoices. Software vendors had to adapt their systems to the new specifications, which often required significant changes to application code.
The documentation of changes compared with FA(2) contains a detailed comparison of both structures, allowing developers to identify precisely all areas that need to be modified in existing systems
The supporting materials for developers contain practical implementation examples and solutions to the most common technical problems. They are valuable support for development teams adapting systems to the new structure.
The structure contains additional data fields, changed formats for recording information and new validation rules. All these elements had to be carefully analysed and implemented in accounting systems.
Testing the adapted systems was crucial for them to work properly after 1 February 2026. The test and pre-production (Demo) environments provided by the Ministry of Finance are used for testing, including for the KSeF 2.0 Taxpayer Application (from 15 November 2025).
Example: a large accounting office serving more than 200 clients started preparing for FA(3) in June 2025. A project team was set up, which reviewed all the systems in use, started working with software vendors and drew up an implementation schedule. Thanks to starting early, the office completed its preparations before 1 February 2026.
Sources of information and documentation
The Ministry of Finance and KAS (National Revenue Administration) provide official information channels on the FA(3) structure. Up-to-date information, documentation and technical files are available on government websites.
KAS announcements are the main source of information about changes to the system. They contain both technical information and practical guidance for different groups of KSeF users.
The ksef.podatki.gov.pl website is the main source of up-to-date technical documentation and information materials on the FA(3) structure, including the brochure describing the fields. Official publications are available free of charge
Regularly checking official sources lets you follow changes to the technical documentation and announcements about a KSeF failure or unavailability, on which the deadlines for sending invoices depend (Articles 106ne–106nh of the VAT Act).
Businesses and accounting offices should also follow announcements from their accounting software vendors, who often publish additional information materials and guidance on preparing for changes.
Taking part in industry conferences and training on e-invoicing can be an additional source of practical knowledge about implementing the new structure. Such events also make it possible to share experience with other system users.
Preparing for implementation
Preparation for issuing invoices in the FA(3) structure should start well before the date the obligation applies – today this concerns especially businesses that move to KSeF only on 1 January 2027. Effective preparation requires a systematic approach that covers technical and organisational aspects.
The first step should be a detailed review of the accounting systems currently in use. This analysis will identify the areas that need modification and help estimate the scope of adaptation work.
Starting preparations for FA(3) early helps avoid problems caused by software vendors being overloaded just before the end of the transitional period on 31 December 2026
Communication with software vendors should cover not only update release schedules but also technical support during implementation. It is worth agreeing detailed terms for technical assistance and the availability of specialists if problems arise.
Preparing user teams to work with new functions requires properly planned training. Training should cover both the technical side of using the systems and the changes in accounting procedures resulting from the new structure.
- Review current accounting systems
- Contact software vendors about update schedules
- Analyse the impact of the changes on existing accounting processes
- Draw up an implementation plan that includes system testing
- Prepare a user training programme
- Set up technical support procedures for the implementation period
- Carry out functional tests before the mandatory implementation date
Outlook for KSeF
The introduction of the FA(3) structure was another stage in the development of the National e-Invoicing System, which is steadily expanding its functionality. Together with FA(3), KSeF 2.0 went live on 1 February 2026, and KSeF 1.0 was switched off.
The legislative work has been completed: the rules of mandatory KSeF are set out in the VAT Act as amended on 16 June 2023 (Journal of Laws (Dz.U.) 2023 item 1598) and 5 August 2025 (Dz.U. 2025 item 1203), and permissions and authentication in the regulation of the Minister of Finance and Economy of 12 December 2025 (Dz.U. 2025 item 1815). The next important date is 1 January 2027: the end of the transitional exceptions (Articles 145m and 145n) and the start of financial penalties (Article 106ni).
The development of KSeF covers not only technical aspects but also legislation. Technical changes, such as new versions of the structure, must be aligned with legal regulations and are announced in advance
In the future, KSeF may include additional functions supporting the automation of accounting processes and integration with other public administration systems. Such solutions could significantly simplify businesses' reporting obligations.
International trends in e-invoicing point to the growing importance of standardisation and system interoperability. The Polish FA(3) structure may be developed in line with European e-invoicing standards, which would make international trade easier.
Continuous improvement of KSeF requires ongoing dialogue between the Ministry of Finance, businesses and software vendors. User feedback is key to identifying areas that need further improvement.
Once the FA(3) structure has stabilised, further changes to KSeF may focus on greater process automation and integration with banking systems and e-commerce platforms. In the future, such solutions could significantly reduce the administrative burden on businesses related to handling electronic invoices.
