After several postponements and an intensive technical preparation phase, mandatory B2B electronic invoicing in Poland is now a reality.
The National e-Invoicing System, known as KSeF (Krajowy System e-Faktur), became mandatory on February 1, 2026, for large taxpayers and was extended on April 1, 2026, to all VAT-registered businesses, with an additional phase for micro-taxpayers scheduled for January 1, 2027.
KSeF 2.0 represents a significant shift in how companies issue, receive, validate, and store invoices in Poland. Its main objective is to centralize the exchange of structured invoices, enhance transaction traceability, and strengthen tax control through a digital environment connected to the Polish tax authorities.
What is KSeF and how does it work?
KSeF, short for Krajowy System e-Faktur, is Poland’s centralized national e-invoicing platform. Through this system, companies must issue and receive structured electronic invoices in accordance with the schema defined by the Ministry of Finance.
The general workflow is as follows:
- The invoice is generated from the company’s ERP, financial system, or invoicing solution.
- The document is prepared in XML format according to the applicable logical structure.
- The invoice is sent to KSeF via the system’s API.
- KSeF validates the document and assigns it a unique identifier.
- Once accepted, the invoice becomes available to the recipient within the system.
- The platform generates acknowledgments and responses regarding acceptance, rejection, or technical issues.
This model positions KSeF as the central hub for B2B invoice exchange in Poland. An invoice is no longer just a document exchanged between companies, but a structured data record validated within a centralized tax infrastructure.
Mandatory e-invoicing timeline in Poland
The rollout of KSeF has been structured in phases to facilitate adoption by businesses and technology providers. Key milestones include:
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January 2022. Start of the voluntary phase. Companies could issue structured invoices via KSeF.
- June 2025. Publication of KSeF 2.0 technical documentation and FA(3) logical structure.
- February 2026. Mandatory for large taxpayers with turnover exceeding PLN 200 million (approx. €46 million).
- April 2026. Mandatory for all VAT-registered businesses, except certain micro-taxpayers.
- April 2027. Mandatory for smaller taxpayers with defined tresholds.
From January 1, 2027, micro-taxpayers whose transactions involve small amounts—such as PLN 450 per invoice and a monthly sales value of PLN 10,000—will also be required to comply with KSeF.
This timeline highlights the importance of proactively reviewing invoicing systems, technical integrations, and internal approval and submission processes.
Key features of KSeF 2.0
The second version of KSeF introduces several enhancements aimed at facilitating mandatory adoption and improving operational efficiency for businesses, integrators, and software providers. Key updates include:
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Introduction of the FA(3) logical structure, effective from February 1, 2026.
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Updated technical documentation for the KSeF 2.0 API.
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Permanent availability of the optional offline24 mode.
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Confirmation of the ability to attach supporting documents to certain e-invoices.
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Temporary continuation of issuing invoices via cash registers until the end of 2026.
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Postponement of the requirement to include the KSeF number in invoice payments until the end of 2026.
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Optional issuance of electronic invoices to consumers.
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Development of authentication mechanisms and certificates for issuing invoices during system downtime.
These measures aim to ease the transition to the mandatory model and reduce technical friction during integration.
Technical update: KSeF specifications version 5.5.1.v1
The Polish Ministry of Finance has released version 5.5.1.v1 of the KSeF technical specifications, introducing improvements designed to optimize system interfaces and facilitate API integration.
One of the most notable changes is the removal of error code 99 associated with HTTP 400 (Bad Request) responses. This update simplifies error handling in KSeF integrations by providing clearer and more consistent responses aligned with expected technical scenarios.
Additionally, the new version introduces the option to use the “kwota przychodu” (revenue amount) parameter as an authorization method in certain schemes. This expands the available authentication options for users and applications interacting with the platform.
Although this update does not introduce new regulatory obligations, it requires attention from developers, software providers, and API integrators. Ensuring compatibility with the latest system version is essential to avoid technical issues in invoice submission, validation, and receipt.
With this update, Poland continues to refine the technical infrastructure of KSeF, strengthening the stability, interoperability, and overall performance of the e-invoicing ecosystem.
FA(3) Format and Invoice Validation
With the implementation of KSeF 2.0, the FA(3) logical structure replaces the previous FA(2) version. This structure defines the XML format that electronic invoices must follow when submitted to the system.
For businesses, this change has significant technical implications. Generating a PDF or visually readable invoice is no longer sufficient. The document must comply with the XML schema required by KSeF to be validated and accepted.
Therefore, ERP systems, invoicing solutions, and document exchange platforms must be capable of:
- Generating invoices in compliance with the FA(3) structure.
- Sending documents to KSeF via the appropriate API.
- Managing system responses, acknowledgments, and rejections.
- Recording the KSeF identification number assigned to each invoice.
- Maintaining full process traceability.
- Handling technical contingencies and offline scenarios.
Structured data is the foundation of the new model, enabling automated validation, reducing errors, and ensuring consistent, machine-readable tax information.
Self-Billing in KSeF
Self-billing processes require particular attention under KSeF 2.0. Companies must adapt their internal workflows to ensure that structured invoices are properly approved before being submitted to the system.
The key point is that approval must be performed on the XML file itself, not on a draft or PDF representation. While a PDF may serve as a reference document, it does not constitute fiscal approval of the structured invoice.
Offline24 mode and contingency scenarios
KSeF 2.0 includes the offline24 mode, which allows invoices to be issued in situations where immediate submission to the system is not possible.
The introduction of this feature as a permanent option provides greater operational flexibility, especially for companies affected by technical issues, connectivity disruptions, or temporary system unavailability.
However, using offline24 requires well-defined internal procedures. Companies must ensure that invoices issued offline are subsequently submitted to KSeF within the required deadlines and that full traceability is maintained from issuance to final validation.
How companies should prepare for KSeF?
Adapting to KSeF is not just a tax compliance project—it impacts technology, finance, administration, accounts payable, accounts receivable, and document management.
Companies should review:
- ERP systems and invoicing solutions.
- XML generation in compliance with FA(3).
- Integration with the KSeF API.
- Validation of customer and supplier master data.
- Self-billing processes.
- Handling of rejections and corrective invoices.
- Storage of acknowledgments and traceability records.
- Offline scenarios and contingency plans.
- Internal approval workflows.
- Coordination between local and corporate teams.
For multinational groups, this review should be approached from a multi-country perspective. Poland is part of a broader European trend toward structured e-invoicing, digital reporting, and system interoperability.
In Poland, transitioning to KSeF requires a combination of regulatory expertise, technical capability, and seamless integration with existing business systems. The SERES platform enables companies to manage e-invoicing processes, document exchange, ERP integration, traceability, and multi-country compliance within a scalable and future-ready environment.
