The mandatory National e-Invoicing System (KSeF) has applied to sole proprietorships in Poland since 1 April 2026. In practice this means that a sales invoice only exists once it reaches the system and receives a KSeF number. That raises a question which previously mattered little: what should you do when there is no connection to the system at the moment of sale — because the client's internet is down, because the Ministry of Finance has announced planned maintenance, or because the system simply does not respond? The regulations provide several separate modes for such situations, and each has its own deadline for submitting the document.
Four modes instead of one exception
The Polish VAT Act does not recognise a single, universal "emergency mode". It distinguishes four situations: offline24 mode, offline mode linked to KSeF unavailability, emergency mode following an officially announced system failure, and total failure. The first three share the same logic — the invoice is issued according to the applicable logical structure template, handed to the buyer outside the system, and then submitted to KSeF. The issue date remains the date shown on the invoice, not the moment the document reached the system. The differences concern the reason for using a given mode and — most importantly in practice — the deadline for submission.
Offline24 — the simplest everyday safeguard
Offline24 mode is voluntary and requires neither a failure nor any official approval. A business owner can use it at any time, for example when issuing an invoice at a client's premises, at a trade fair, or in the field without coverage. The invoice is handed to the buyer immediately and submitted to KSeF no later than the next business day after the day of issue. The name can be misleading: this is not 24 clock hours but the following business day, and the deadline runs from the issue date entered on the invoice — not from the moment you get round to sending it. For many sole traders this is the most convenient way to work, because it makes invoicing independent of connection quality.
Unavailability and failure — two different clocks
Offline mode linked to KSeF unavailability applies to announced interruptions, which the Ministry of Finance communicates through the interface software. Invoices issued during that time must be submitted no later than the next business day after the day on which the period of unavailability ends — what counts is therefore the end of the interruption, not the invoice issue date.
Emergency mode works differently. It applies once a KSeF failure has been announced in the Ministry of Finance's Public Information Bulletin (BIP) and in the interface software. In that case there are 7 business days from the day the failure ends to submit the invoices. One detail is worth remembering: if an invoice was issued in offline24 mode and a failure is announced before it has been submitted, the longer emergency deadline applies. For that reason someone in the business should keep track of system availability announcements — otherwise it is easy to confuse the two regimes and miss the submission deadline.
Total failure — a temporary return to paper
Total failure is intended for extraordinary situations in which an announcement can be published neither in the BIP nor in the interface software. The information is then distributed through mass media — television, radio, press or the internet. During such a failure the business owner issues the invoice on paper or electronically in any format, without having to apply the logical structure template. Importantly, once the total failure ends these invoices do not have to be submitted to KSeF at all. It is the only mode in which the document never enters the system — and the only one in which the invoice handed to the buyer is not marked with QR codes.
QR codes and the KSeF certificate
Invoices issued in offline24 mode, offline mode or emergency mode and handed to the buyer outside the system must carry two QR codes. The first, labelled "OFFLINE", allows the invoice to be located in KSeF and its data to be verified. The second, labelled "CERTYFIKAT" (certificate), confirms the identity of the issuer at the moment the document was issued.
Generating the second code requires a KSeF certificate. The application is submitted after logging into the KSeF Taxpayer Application or via the API, authenticating with, among other options, the Trusted Profile (Podpis zaufany) or a qualified electronic signature. The certificate serves solely to confirm identity — invoicing permissions are granted separately — and it is valid for a maximum of two years. It is worth obtaining it in advance, because there will be no time for that once a failure occurs. From 1 January 2027 certificates are set to replace the existing tokens entirely.
What to do in your business now
Preparation comes down to a few simple steps. First, check whether your invoicing software genuinely supports the special modes, can generate both QR codes and tracks the submission deadline itself. Second, apply for a KSeF certificate and store it securely. Third, decide who in the business monitors unavailability and failure announcements, and who is responsible for submitting outstanding invoices. It is also worth rehearsing the procedure calmly, rather than learning it on the day the system stops responding.
QR codes have one more practical use: they let the buyer check whether the document received actually matches the invoice registered in KSeF. If you run a business and receive offline invoices, it is worth using that option — it is a simple way to spot a document that has been swapped or issued by someone other than the letterhead suggests.