On 2 February 2026 — the first working day of mandatory KSeF — thousands of companies tried to log in at once, and Profil Zaufany (the "Trusted Profile," Poland's government login) stopped responding. The KSeF engine itself worked fine; the bottleneck was authentication through Profil Zaufany, which buckled under the load. Poland's finance minister later confirmed that heavy login demand coincided with a DDoS attack launched simultaneously from 17 countries.
The lesson for any business is simple: government gateways will go down sometimes, and you still have to issue your invoice. That's exactly what offline24 mode is for — and despite the name, it isn't a "break-glass-in-emergency" tool. It's your everyday right to keep working without a connection. This article breaks it down.
"KSeF is down" vs "I can't log in" — not the same thing
Start with the distinction that saves you from a costly mistake. February 2026 showed that "KSeF is down," in most people's minds, usually means "I can't log in via Profil Zaufany." Those are two different problems — and which special mode applies to you, and how long you have to upload, depends on what actually happened.
Problem on your side (no internet, your software won't respond, KSeF is slow) → offline24 mode. You use it on your own initiative, without waiting for any announcement. The law does not require you to prove you had a connection issue.
The Ministry of Finance announces unavailability or an outage in BIP MF (the Ministry's official public bulletin) → offline mode (planned downtime) or emergency mode (sudden outage). These are triggered by an MF announcement, not by you.
In February, MF did not declare a KSeF outage in BIP — because the invoicing system itself was working. Authentication failed. In practice that meant the right tool was offline24: your own decision to issue locally and upload the next day. And companies working through their own software, integrated via API and a certificate, barely noticed the Profil Zaufany problem at all.
Four modes for when "online" isn't working
Polish law foresees four ways of working outside online mode. They differ by cause, upload deadline, and how you hand the invoice to the buyer. Here's the cheat sheet:
Mode When Deadline to upload to KSeF offline24 Your initiative: no internet, software issue, KSeF slow next business day after the issue date offline (unavailability) MF announces planned downtime in BIP MF next business day after the downtime ends emergency MF announces a sudden outage in BIP MF and via API 7 business days from the end of the outage total outage Extraordinary event (e.g. infrastructure paralysis), announced in mass media invoices are not uploaded; paper/PDF without FA(3) is allowed
The most common error is confusing "1 day" with "7 days." Remember: offline24 and planned unavailability = next business day; an MF-declared outage = 7 business days. The reverse mistake — waiting for MF to declare an outage when your router has simply died — just costs you time and sales. You're entitled to offline24 immediately.
MF documents the full procedures on its pages for offline24 mode and offline mode — KSeF unavailability.
offline24 mode, step by step
1. Issue the invoice in the FA(3) structure
Even with no connection to KSeF, the invoice must be an XML file matching the FA(3) schema (the structured e-invoice format in force since 1 February 2026). You can't send your customer a photo of a handwritten note — that's legal only during a total outage.
2. Mind the issue date
The issue date is the date you enter in field P_1 of the structure — not the date KSeF comes back and accepts the document. The invoice has legal force from the moment you issue it.
3. Add the QR codes
An invoice handed to the buyer outside KSeF (before it gets a KSeF number) carries two QR codes: the first ("OFFLINE") gives access to the invoice in KSeF and lets the buyer verify its data; the second ("CERTYFIKAT") confirms the issuer's identity. To generate the second one you need a KSeF type 2 certificate (the offline certificate). You download it from the official KSeF Taxpayer App or via API; it's valid for 2 years — and you need it before the connection drops, because you won't be able to fetch it once it's down.
4. Deliver the invoice to the buyer — depending on who they are
A domestic Polish VAT payer with a NIP (tax ID) receives the invoice through KSeF — formally only once it has a KSeF number. Until then you can issue a transaction confirmation (a temporary document provided for in the rules).
A foreign buyer, a consumer, or a buyer with no NIP (Article 106gb(4)) receives the invoice through an agreed channel (email, portal). The receipt date is the actual date they receive it. For foreign-owned companies invoicing counterparties abroad, this is the path you'll most often use.
5. Upload to KSeF by the next business day at the latest
Once uploaded, the invoice gets its KSeF number — and that number is what matters for tax purposes. You can only issue a correction to an offline24 invoice after the original has been uploaded and assigned a number. The order is fixed: original → KSeF → number → correction.
Common traps
From talking to business owners and from how offline handling plays out in practice, a few mistakes recur:
Waiting for an MF announcement when it's your own internet that failed. Don't wait — switch to offline24 yourself.
No type 2 certificate. Without it you can't generate the second QR code, and the offline invoice is legally just a draft. Download the certificate ahead of time.
Paper instead of FA(3). A plain PDF or printout instead of the FA(3) structure is allowed only during a total outage.
Mixing up the 1-day and 7-day deadlines. Getting it wrong risks a penalty — but only from 2027.
Issuing a correction before uploading the original. Without the original's KSeF number, you can't correct it.
An empty KSeF number field in JPK_V7. The number must be filled in after assignment — your software should do this automatically.
Good news for 2026: no financial penalties will be imposed for KSeF errors this year — they start only on 1 January 2027. From that date the sanctions under Article 106ni of the VAT Act (up to 100% of the invoice's VAT) also kick in. Treat 2026 as time to master the process calmly — but build the habits now.
How Biurko handles offline24 for you
All of this sounds complex enough that it's easy to slip up under pressure. So at Biurko we turned it into a process that runs on its own:
Automatic outage detection. When KSeF stops responding, Biurko switches transmission into offline24 mode after a few failed attempts, instead of hammering a gateway that's already down.
A compliant document, generated for you. The invoice is produced as validated FA(3) XML, with a verification code and a QR code on its visualisation — and the upload deadline shown on the document.
Deadline tracking. If the deadline passes and the invoice still hasn't reached KSeF, Biurko marks it "needs review" and notifies you and the invoice's author. Nothing slips through silently.
Automatic resubmission on recovery. When KSeF comes back, queued invoices are uploaded automatically — no clicking through them one by one.
Certificate-based authentication, not Profil Zaufany. That's the same difference that, in February 2026, separated companies that kept working from those locked out at the gateway. Biurko also monitors your certificate's validity and warns you 7, 3, and 1 day before it expires.
Checklist for a KSeF outage
Download your KSeF type 2 certificate now and store it securely (don't wait for the connection to fail).
Confirm your software issues offline invoices in FA(3) with both QR codes — test it on the test environment.
Agree a delivery channel for offline invoices with key buyers (email, portal) so there's no dispute over the receipt date.
Memorise the deadlines: offline24 and planned unavailability = next business day; an MF outage = 7 business days.
Bookmark a way to check KSeF status, so you know whether it's the system or your own connection.
Assign someone in your company to own the next-day upload of offline invoices.
Wrap-up
offline24 isn't a doomsday mode — it's your everyday safety net for when the network or the government gateway refuses to cooperate. You issue the invoice in FA(3), add the QR codes, deliver it to the buyer, and upload it to KSeF by the next business day at the latest. The rest is discipline and a good tool.
Biurko takes that discipline off your plate: it detects the outage, switches modes, tracks the deadline, and uploads your invoices once KSeF returns. Want to test it on your own invoices? Create an account and try Biurko free for 14 days — no card required, full offline24 mode included.
FAQ
Can I issue invoices when KSeF is down? Yes. Use offline24 mode (when the problem is on your side) or offline/emergency mode if MF announces unavailability or an outage in BIP. You issue the invoice in the FA(3) structure, add the QR codes, and upload it to KSeF within the applicable deadline.
How long do I have to upload an offline24 invoice? By the end of the next business day after the issue date, at the latest. That's a shorter window than emergency mode (7 business days), which is why people confuse them — offline24 is always the next business day.
How is offline24 different from emergency mode? You trigger offline24 yourself when you have no internet or your software fails — no announcement needed. Emergency mode applies only once the Ministry of Finance declares a KSeF outage in BIP, and it gives you 7 business days to upload instead of one.
What is a KSeF type 2 certificate? It's the offline certificate you use to mark an invoice with a code confirming your identity as the issuer (the second "CERTYFIKAT" QR code). You download it from the KSeF Taxpayer App or via API; it's valid for 2 years. Without it, you can't issue an offline invoice compliantly.
Are there penalties for a late offline invoice? Not in 2026 — it's a transition period with no financial penalties. Sanctions for KSeF errors, including missing the upload deadline, take effect on 1 January 2027 (up to 100% of the invoice's VAT). That's why 2026 is the time to build your procedures.