Mandatory KSeF in 2026: Comprehensive guide to legal, organizational and technical implementation

Part 1: The New KSeF Landscape: A Strategic and Pragmatic Re-Launch

The introduction of the National e-Invoice System (KSeF) in Poland is undergoing a fundamental transformation. The original vision of implementation, based on the “big-bang” model, has given way to a more flexible, phased and consultative approach. This change is not just a technical correction, but a strategic reset, forced by technological realities and dialogue with the market. Understanding the genesis and nature of this new opening is crucial for any company preparing for mandatory e-invoicing in 2026.

1.1 Introduction: From Technical Failure to Collaboration and a Fresh Start

The main and direct reason for postponing the original KSeF implementation date, planned for 2024, was diagnosed critical system performance issues. Analyses and audits showed that the system architecture was unable to process the huge number of invoices that were supposed to flow into it, estimated at millions in short periods of time.1 This technical failure undermined confidence in the project and forced the Ministry of Finance to fundamentally revise its strategy.

In response to the crisis, the ministry took unprecedented action. Instead of imposing further deadlines, it initiated wide-ranging public consultations, in which, as indicated by the Regulatory Impact Assessment (RIA) documents, a total of around 10,000 people representing various sectors of the economy took part.1 Numerous industry organizations, chambers of commerce and associations of accountants and tax advisors were involved in the process.1 This intensive dialogue, conducted since February 2024, has identified key barriers and concerns of entrepreneurs.

The result of this cooperation is a completely new legislative environment. The draft laws and regulations of June 2025 are no longer just a technical patch for the old system, but a comprehensive response to market demands. They introduce a number of simplifications, transitional mechanisms and flexible solutions that are intended not only to ensure the technical stability of the KSeF, but also to facilitate adaptation on the part of taxpayers.1 There is a visible change in philosophy – from rigidly imposing an obligation to building a system in a more pragmatic and user-oriented way. This evolution from a technical failure to a collaborative model is a key context that defines the current shape and timeline of the KSeF implementation. This suggests that future digital initiatives of the tax administration may follow a similar, more partnership-based path, which is an important strategic information for the business.

1.2. Final Implementation Roadmap: Phased Approach

The new regulations introduce a clear, two-stage schedule for implementing the mandatory KSeF. This is a direct implementation of the system audit recommendations, aimed at spreading the load and ensuring the technical stability of the platform during the critical start-up period.1

Phase 1: February 1, 2026

The obligation to issue structured invoices will be the first to cover large enterprises. According to the act, the criterion for qualifying for this group is the value of sales (including tax), which in 2024 exceeded PLN 200 million. It is estimated that this phase will apply to about 5 thousand of the largest taxpayers in Poland.1

Phase 2: April 1, 2026

Two months later, the KSeF obligation will be extended to all other entrepreneurs. This will include both active and exempt VAT payers, regardless of the scale of their business.1 This additional period is intended to give smaller entities, often with fewer resources, more time to prepare systems and processes.

However, the full roadmap for implementing KSeF is not limited to these two dates. The legislator has precisely defined a number of other key dates that create a comprehensive calendar for preparations and the entry into force of individual functionalities and obligations:

• November 1, 2025: This is a key date for the technical and implementation teams. From this day on, taxpayers will have early access to two fundamental tools:

• KSeF Certificate: Possibility to download a special certificate, necessary to use the new offline modes.
• KSeF 2.0 test environment: Launching a new version of the test environment that will reflect the target functionalities of the mandatory system will allow for real integration testing.1

• January 1, 2026: Entrepreneurs who, due to the specific nature of their business (e.g. media, telecommunications industry) need to send extensive invoice data will be able to submit applications for the use of the new functionality from that day on. invoices with attachment.1
• January 1, 2027: This is the date of activation of deferred obligations and sanctions. From this day:

• The obligation to provide the KSeF invoice number in the title of the transfer (both standard and in the split payment mechanism) will come into force.
• Financial penalties will begin to be applied for failure to comply with KSeF-related obligations.1

The table below synthesizes the entire implementation sequence, providing a practical tool for project planning within the organization.

Table 1: Key Dates and Milestones of KSeF Implementation

Part 2: Navigating the Legal and Organizational Framework

The new KSeF legislation, although comprehensive, was designed based on the principle of technical pragmatism. It precisely defines the scope of the obligation, but at the same time introduces a number of deliberate exclusions, simplifications and transitional periods. Understanding these nuances is essential for the correct adjustment of business processes and avoiding unnecessary costs and the risk of non-compliance.

2.1. Scope of the Obligation: Who is included, who is excluded and why?

In principle, from 1 April 2026, the obligation to issue structured invoices via KSeF will cover practically all VAT payers - both active and exempt - who carry out transactions that require documentation with an invoice in accordance with the VAT Act.1

However, the legislator has provided a catalogue of permanent exemptions from this obligation. An analysis of the draft regulation on exemptions and its justification shows that these decisions were not dictated by industry pressure, but by hard technical and procedural arguments that prevent the use of KSeF in certain business models.1

Key areas excluded from the KSeF obligation are:

• Passenger transport services and motorway tolls: The exclusion applies to services documented by single tickets (e.g. train, bus, plane) and receipts for toll motorway travel, which are considered invoices under separate regulations. The justification here is the specificity of these services: a huge number of low-value transactions, the need to ensure maximum speed of service at the point of sale and the variety of distribution channels. The requirement to obtain a KSeF number for each ticket in real time would paralyze these processes.1
• Selected financial and insurance services: The obligation to document services exempt from VAT under Article 43, paragraph 1, point 7, 37-41 of the VAT Act has been excluded. This applies to, among others, banking, insurance, credit granting and financial instrument management services. These industries are subject to separate, strict regulations and have specific, often automated systems for generating documents (e.g. accounting notes), the integration of which with KSeF would be disproportionately complicated and expensive.1
• Cross-border self-billing: This is the most technically complex exclusion. It concerns the situation in which the invoice is issued on behalf of and for the benefit of the Polish seller by the buyer (in accordance with the self-billing agreement), who for the purposes of this specific transaction is not identified by a Polish NIP number. This is a fundamental technical barrier, because the entire authentication and authorization system in KSeF is based on the Polish NIP. Without it, a foreign buyer cannot obtain authorization to issue invoices in the system on behalf of a Polish supplier.1
• Optional use of KSeF in self-billing: At the same time, in a bid for flexibility, the regulations provide for possibility (but not obligation) using KSeF in the self-invoicing procedure, if the foreign buyer uses a VAT-UE number. In such a case, the Polish seller will be able to grant him appropriate authorizations in the system. This shows that where there is a technical possibility of identifying the entity, the legislator opens the door to voluntary integration.1

This technical pragmatism sends an important signal to business: any future demands for changes to the KSeF will need to be supported by solid procedural and technical arguments, not just economic ones.

2.2. Easing the burden: Key transitional provisions and simplifications

Aware of the scale of the challenge posed by the implementation of the KSeF, the legislator has introduced a number of protective mechanisms and simplifications that are intended to ease the burden, especially in the initial period of operation of the system.1

The most important of them are:

• Temporary exemption for micro-entrepreneurs: In the period from April 1, 2026 to December 31, 2026, taxpayers will be able to continue issuing invoices in their current form (paper or electronic), provided that the total value of sales documented by these invoices in a given month does not exceed PLN 10,000. This right expires in a given month at the time of issuing an invoice that exceeds this threshold. This is a direct nod to the smallest companies and "digitally excluded" people, for whom immediate implementation of KSeF could be an insurmountable barrier.1
• Extended period for cash registers: The possibility of issuing simplified invoices (receipts with the buyer's Tax Identification Number) and full invoices using cash registers will be maintained until December 31, 2026.1 This is key information for the retail sector, giving additional time to adapt or replace sales devices and systems.
• Deferred payment identification obligation: One of the most complex operational requirements – the obligation to provide the KSeF invoice number in the title of the transfer (both standard and under the split payment mechanism) – has been postponed until January 1, 2027.1 This is a significant simplification that gives companies over a year of additional time to adapt their accounting systems, banking systems and payment reconciliation processes.
• Deferred sanctions: In parallel, to January 1, 2027 the application of financial penalties for breaches of KSeF obligations, such as failure to issue a structured invoice or sending it to the system after the deadline, has also been postponed.1 This creates a “grace period” during which entrepreneurs can implement and stabilize their processes without the risk of immediate financial consequences.

2.3. Transformation of key billing scenarios

The new regulations significantly change the handling of several key, everyday invoicing scenarios.

• Consumer Billing (B2C): The original plan to completely exclude consumer invoices from the KSeF was abandoned in favor of the model optional.1 This means that if a consumer (an individual who does not run a business) requests an invoice, the seller has a choice: he can issue a traditional invoice (paper/PDF) or, if it is more convenient for him, he can issue a structured invoice in KSeF.

• What is important, issuing a KSeF invoice for the consumer does not require his consent.1
• However, the seller is obliged to provide the consumer with access to this invoice. This can be done by providing them with a printout or a PDF file with a special QR code, or by providing the code itself and the data necessary for so-called "anonymous access" to the invoice in the KSeF system.1 This solution significantly simplifies processes in companies serving both business customers (B2B) and individual customers (B2C), allowing them to unify their invoicing system.

• Agricultural invoices (VAT RR): Integration of VAT RR invoices with KSeF will also be optionalThe possibility of issuing them in the system will appear from April 1, 2026.1 The buyer of agricultural products, after obtaining consent from the flat-rate farmer, will be able to issue these invoices on his behalf directly in KSeF. The system will support this type of document, including new offline modes of work, which gives agriculture a modern tool for documenting transactions.1

Part 3: Technical overview: KSeF system architecture and new functionalities

The amendment to the KSeF regulations introduces revolutionary changes to the technical layer of the system. These are not just cosmetic improvements, but fundamental new architectural concepts, such as dedicated certificates, offline work modes or attachment support. Understanding these mechanisms is absolutely crucial for IT directors, system architects and developers responsible for integrating ERP and accounting systems with KSeF.

3.1. Authentication and Authorization: The New Credential Landscape

The KSeF system is moving from a simple authentication model to a more granular and secure credential management system. The main identification and authorization methods in the system are 1:

• National Node of Electronic Identification: It includes popular methods such as Trusted Profile, enabling individuals to authenticate themselves.
• Qualified Signature or Electronic Seal: A corporate standard used to mass authenticate automated processes and grant authorizations on behalf of the company.
• New KSeF Certificate: This is the most important and completely new element in the security architecture. It is a special, dedicated certificate (authorization token) that is generated by the taxpayer after successful authentication one of the above methods. Its main and key goal is to enable work in new offline modes. It allows for local, cryptographic signing of an invoice, which guarantees its authenticity of origin and integrity of content before it is sent to KSeF.1 This certificate has a 2-year validity period and can be renewed during its validity.1
• Transition period for old tokens: The existing alphanumeric authorization token used in the optional system will be able to be used for authentication until December 31, 2026. However, there is a critical limitation: it will not be possible to generate a new KSeF Certificate using it.1 This means that companies that only use old tokens will not be able to use offline modes and will need to plan for migration to new authentication methods.

Authorization management (who can issue invoices, who has access to them) is mainly done via the KSeF API. However, for entities that do not have the possibility to use electronic methods (e.g. foreign companies without a Polish representative office), the possibility of granting the first authorizations to one indicated natural person using a paper form has been maintained ZAW-FA, submitted to the tax office.1

Table 2: Authentication Methods in KSeF and Their Applications

3.2. "Offline24" mode: A new paradigm of e-Invoicing

The introduction of the “offline24” mode, defined in the new Article 106nda of the VAT Act, is one of the most important technical changes in the entire project.1 This is a permanent and voluntary method of operation that fundamentally transforms KSeF from a pure “clearance” system (where an invoice legally exists only after being approved by the system) to a hybrid model.

The architecture of this process is as follows:

1. The taxpayer generates an invoice locally in your system (e.g. ERP), in standard XML format compliant with the FA(2) schema.
2. The invoice is legal "exposed" with the date indicated by the taxpayer in its content (in accordance with field P_1), and not with the date of submission to KSeF.1
3. The taxpayer is obliged to send this invoice to KSeF immediately, but no later than the next business day after the date of its issue.1
4. After successful uploading to the system, the invoice receives its unique KSeF number and is made available to the buyer (if they use KSeF).

This mode is designed to secure business continuity in the event of local technical problems on the taxpayer’s side, such as an Internet failure, ERP system failure or power outage.1 Implementing this architectural duality – synchronous online and asynchronous offline – is the biggest challenge for integrators. It requires designing two separate invoice lifecycles in the company’s systems, which has implications for internal controls, audit trails, and error handling logic (e.g. what happens if an invoice issued offline is not loaded correctly the next day).

3.3. Attachments to e-Invoices: Response to submitted billing data

The new attachment handling functionality is a direct response to the demands of industries (including energy, gas, telecommunications) that could not fit all the required or commonly provided data into the standard invoice structure, e.g. detailed billing of consumption from multiple collection points.1

The rules and process for using attachments are strictly defined 1:

1. Prior registration requirement: In order to send invoices with an attachment, the taxpayer must first submit an appropriate application via the e-Tax Office portal. Consent to use this functionality is issued for a period of 2 years.
2. Content restrictions: The attachment must be in the form of a structured XML file and may only contain data that is an extension of the mandatory elements of the invoice (e.g. detailed data on the measure, quantity, unit price). It is strictly forbidden to include marketing, advertising or other data unrelated to the transaction in attachments.
3. Technical limitations: One invoice can only have one attachment, and the total size of the invoice with the attachment cannot exceed 3MB.
4. Control mechanism: The KSeF system will have mechanisms for verifying the content of attachments. If abuse is detected (e.g. sending prohibited content), the taxpayer may be automatically denied the right to use this functionality.

3.4. Visualization and verification: Multi-layer QR code system

The new regulations introduce an advanced system for marking invoices that are processed or presented outside of KSeF (e.g. as a printout or PDF file). The aim of this system is to ensure an inseparable connection of each visualization with its digital original in KSeF and to guarantee its authenticity and integrity.1

This system is based on two main scenarios:

Scenario 1: Standard structured invoice, made available outside KSeF (e.g. PDF for the consumer):

• Code 1 (QR verification code): It contains a unique link to the invoice resource in KSeF, the seller's NIP, the date of issue and a unique abbreviation (hash) of the invoice content, the so-called invoice distinguisher. This allows for quick online verification of whether a given visualization corresponds to the original in the system.
• Label 1 (KSeF Number): The full, legible number identifying the invoice in KSeF must be placed directly under the QR code.

Scenario 2: Invoice issued in failure or offline mode, made available outside KSeF (before sending it to the system):

• Code 1 (QR verification code): Same as scenario 1.
• Label 2 (“OFFLINE”): Additional text label placed below the verification code to indicate that the invoice was generated offline.
• Code 2 (QR Integrity Code): This is a second, separate QR code. It contains data digitally signed using KSeF CertificateIts purpose is to enable verification of the authenticity of origin (whether the invoice was issued by an authorized entity) and the integrity of the content (whether the invoice has not been changed) Before its upload to KSeF.
• Label 3 (“CERTIFICATE”): Text label placed below the integrity code.

This multi-layered coding system is a key element in sealing the system and preventing fraud. It ensures that every physical or digital representation of an invoice can be verified at any time and linked to its authoritative source in KSeF.

Conclusions

The analysis of the latest legislative projects concerning the National e-Invoice System leads to several key conclusions that should shape the implementation strategy of every Polish enterprise.

1. KSeF 2.0 is a revised project, not just postponed: The most important conclusion is to understand that we are dealing with a fundamentally new approach to implementation. The postponement of deadlines is not just a pause, but the result of a strategic reset caused by the technical failure of the original platform. The new KSeF, shaped by broad consultations, is more flexible, pragmatic and focused on business realities. The introduction of a phased implementation, transition periods and numerous simplifications shows that the tax administration has learned from previous experiences.
2. Hybrid architecture requires new thinking about processes: The introduction of a permanent, voluntary "offline24" mode and a dedicated KSeF Certificate creates a dual system architecture. KSeF is no longer just a "clearance" system operating in real time, but also a platform accepting invoices in asynchronous mode. For companies, this means the need to design and implement two parallel invoice processing paths, which has profound implications for ERP systems, internal control and operational risk management.
3. New technical mechanisms are of key importance: The success of the implementation will depend on the correct implementation of completely new technical concepts that did not exist in the previous version of the system. These include: managing the life cycle of the KSeF Certificate, handling invoice attachments while taking into account their limitations and, what is extremely important, implementing a complex, multi-layered system for generating QR codes for invoice visualization. These elements constitute the greatest development challenge.

Recommendations for business:

• Update your implementation strategy: Don't treat the KSeF project as "postponed". Start revising your implementation plans immediately based on new deadlines, requirements and simplifications.
• Prioritize legal analysis: Ensure that your IT and accounting teams are working with the latest draft laws and regulations, not outdated technical documentation.
• Focus on new technical challenges: Direct development resources to analysis and implementation of "offline24" mode, KSeF Certificate management and QR code generation. These are the areas of greatest complexity.
• Take advantage of transitional periods: Actively plan for the use of protection mechanisms. Deferred obligation to mark payments and apply penalties provides valuable time to stabilize systems after they go live. Smaller companies should assess whether they qualify for a temporary shutdown to gain additional time to prepare.

Ultimately, the new KSeF legal framework, while still a huge challenge, creates a more realistic and achievable path to digital invoicing in Poland. Success will depend on a thorough understanding of the new rules and proactive adaptation of strategies, processes and technologies to them.

Sources

1. 12/06/2025 Justification for the regulation on the use of KSeF (7943214).doc
2. documentation changelog – KSeF REST API – integration documentation for KSeF invoices, accessed on June 17, 2025, https://ksef24.com/en/ksef-changelog/
3. KSeF REST API – integration documentation for KSeF invoices, accessed on June 17, 2025, https://ksef24.com/en/
4. generating invoices – KSeF Invoices – KSeF REST API, accessed on June 17, 2025, https://ksef24.com/en/ksef-rest-api-generowanie-faktur/
5. PHP and REST API library for integration with KSeF :: 4programmers.net, accessed on June 17, 2025, https://4programmers.net/Forum/Og%C5%82oszenia_drobne/375602-bilblioteka_php_i_rest_api_do_integracji_z_ksef