KSeF 2026 • stress-free implementation

KSeF is coming.
Prepare your business once and for all.

KSeF is not only about issuing sales invoices. It is also receipt of cost invoices from suppliers. To access them, you need a solution that KSeF can handle correctly and securely.

We have been operating for years

We advise, implement, and train. We focus on simple solutions that operate stably and are ready for KSeF and company growth.

Implementation + support

From installation and configuration to employee training, we're also available post-implementation—when questions arise or your business changes.

Ready for KSeF • No stress • With Pat15.net

What is KSeF and what does it change in companies?

The National e-Invoice System (KSeF) is a government IT system aimed at standardizing the issuance and circulation of invoices in Poland. In practice, this means switching to the so-called. structured invoices (e-Invoices), which have a specific format and are transmitted and stored in the central KSeF system.

For entrepreneurs, KSeF will be a significant change, as it isn't just about "a new invoice design." The system impacts the entire billing process within a company: from issuing a sales document, through its shipment, to receiving and accounting for purchase invoices. Ultimately, e-Invoice will become the standard in billing. B2B, and entrepreneurs will have to adapt their tools, way of working and internal procedures to this.

Importantly, KSeF is not only a sales obligation. It is also a change on the part of cost invoices, i.e. documents coming from suppliers. In practice, the company must be ready not only to "issue" but also receive, verify and archive invoices in the new model. That's why it's so important to have a program that allows you to manage KSeF in a secure, orderly, and compliant manner.

Deadlines for mandatory implementation of KSeF

The mandatory implementation of KSeF is to be introduced in stages – from February 1, 2026. and from April 1, 2026., depending on the size of the company. This means that some companies will become subject to the obligation earlier, while others will become subject to the obligation a few weeks later.

Importantly, from February 1, 2026, companies will have to be ready to receive cost invoices from KSeF. — regardless of the size of your business. In practice, this means that even if your company doesn't issue all its invoices in KSeF yet, it still needs access to the system and a tool that allows receipt and processing of invoices from contractors.

It's worth preparing in advance, because implementing KSeF isn't just about installing the program. It's also about selecting the right solution (e.g. Subiekt 123 or Subiekt nexo PRO), configuration, testing, employee training and ensuring the continuity of issuing and receiving invoices from day one.

The implementation of Subiekt Nexo by pat15.net was quick and seamless. I particularly appreciated the clear explanation of how KSeF works – everything was presented in simple language. The program was immediately ready to use.

Kasia the accountant

We were committed to a smooth launch of Subiekt 123 and preparing the company for KSeF. pat15.net clearly explained all responsibilities and processes, and the implementation itself proceeded without any downtime or complications.

Thomas

DomBud

I was worried about KSeF and the system change, but pat15.net explained everything thoroughly and clearly. Subiekt 123 was implemented very quickly, and the entire process turned out to be easier than I expected.

Jarek Mowicki

Professional implementation of Subiekt Nexo Pro, including preparation for the KSeF. All technical and formal issues were clearly discussed, and the team was able to begin work without any problems from day one.

Wojtek

Manufacturing company

pat15.net efficiently implemented Subiekta Nexo and clearly explained the KSeF processing rules. This ensures that invoices are issued and received correctly. Excellent communication and complete professionalism.

Asia

Administration

Two proven options: Subiekt 123 or Subiekt nexo PRO

We will select a solution that suits your industry, sales method, number of positions, and storage needs.

Subiekt 123 - fast online invoicing (cloud)

Perfect for companies that want to issue documents quickly and from any device.
Data in the cloud - log in wherever you work.
Simple start and clear interface - less implementation pain.
A good choice when speed and simplicity are priorities.

Subiekt nexo PRO - sales and warehouse (extended version)

Sales and warehouse program with integration with KSeF.
Sending, receiving and archiving e-Invoices compliant with requirements.
For companies that need more control and multi-station work.
A great choice for larger scale operations and integrations.

Not sure what to choose? That's normal.

Call us—we'll find the best solution for KSeF and your industry. You'll get specific information: what to buy, how to implement and how long it will take. In the simplest cases, we run the whole thing even in 1 hour.

We also issue CERTUM qualified seals and signatures.

We will select a solution that suits your industry, sales method, number of positions, and storage needs.

Due to the KSeF, more and more companies need to organize not only their invoicing software, but also their identification and authorization issues. That's why at Pat15.net we're publishing qualified electronic signatures and qualified electronic seals Certum.

Both solutions are used to securely confirm the authenticity of documents and company operations in online systems – but their purpose is different:
qualified signature is assigned to a specific person and has the legal force of a handwritten signature,
qualified stamp is assigned to company (organization) and works as a digital equivalent of a company stamp - it confirms that the document comes from a given entity.

We issue signatures and seals remotely in as little as 1 hour (in the simplest cases), and if you prefer, we can also issue on-site at the customer's premises.

Certum qualified electronic signature

Certum qualified electronic signature It's a signature assigned to a natural person that has the same legal force as a handwritten signature. It allows you to sign electronic documents in a way that is unambiguous, secure, and accepted throughout the EU.

In the context of KSeF, a qualified signature is particularly useful when a company needs to formally confirm activities, sign documents and authorizations, or handle processes that require the signature of a responsible person.

At Pat15.net we can issue a signature remotely even in 1 hour, and also on-site at the customer's premises — with setup and start-up assistance.

Certum qualified electronic seal

Certum qualified electronic seal It's the digital equivalent of a company seal—it contains organizational data and is used to confirm the authenticity and integrity of e-documents. It's intended for companies and institutions, not individuals.

In practice, the seal works well where documents should be confirmed "in a company-specific way" - especially with a larger scale of work, automation and orderly document flow in the company (which is very important when implementing KSeF).

We can issue the seal remotely even in 1 hour , or carry out the issuance on-site at the customer's premises along with the configuration.