Since 1 April 2026, mandatory e-invoicing covers effectively all VAT taxpayers in Poland, and from 1 January 2027 financial penalties for breaching KSeF invoicing rules become applicable. Until then, an outage procedure is worth rehearsing rather than merely documenting. Below is the decision tree, the deadlines, and the list of things you must prepare in advance, because you cannot arrange them mid-outage.
Step 1: identify the scenario (30 seconds)
The Polish VAT Act defines four distinct situations, and each carries a different upload deadline. The difference is not a legal nuance. It is the difference between one business day and seven.
Situation Mode Legal basis Deadline to upload to KSeF Problem on your side: no internet, timeout, integration error, poor connection offline24 Art. 106nda of the VAT Act without delay, no later than the next business day after the issue date Ministry of Finance announced KSeF unavailability (scheduled maintenance) in its Public Information Bulletin (BIP) offline (unavailability) Art. 106nh no later than the next business day after the unavailability period ends Ministry of Finance announced a KSeF failure in BIP and in the interface software emergency mode Art. 106nf within 7 business days from the day the failure ends A total failure is announced through mass media total failure Art. 106nf invoices are not uploaded to KSeF at all
Sources: the Ministry of Finance pages on offline24 mode, emergency mode and offline mode during system unavailability.
The practical takeaway: do not wait for an official announcement. Checking BIP takes a minute, but if there is no announcement, offline24 is available to you anyway. It is voluntary, always available, and carries no eligibility restrictions.
Step 2: issue the invoice in offline24 mode
Offline24 is your default move because it does not depend on anyone else's decision. Under Art. 106nda of the VAT Act you issue the invoice electronically, using the applicable FA(3) logical structure, and then upload it to KSeF without delay, no later than the next business day after the issue date.
Three things people routinely get wrong here:
The issue date does not change. The issue date is the one you state on the invoice in field P_1, not the date KSeF finally assigns a number. Issue on Friday, upload on Monday, and the issue date is still Friday.
The KSeF number arrives later, and that is normal. For a buyer who is a Polish VAT taxpayer, the receipt date is the date the KSeF number is assigned, so formal delivery happens after you upload.
You cannot immediately correct an offline invoice. A correcting invoice can only be issued once the original has been assigned its identifying number in KSeF. If you made a mistake on an offline invoice, you must upload it first.
Step 3: the two QR codes that make the document complete
This is where improvised outage procedures usually fall apart.
If you hand the invoice to the buyer outside KSeF, before uploading it, the document must carry two QR codes:
Code I ("OFFLINE") provides access to the invoice in KSeF and lets the buyer verify its data once uploaded.
Code II ("CERTYFIKAT") confirms the identity of the issuer at the moment of issuance.
Generating the second code requires a KSeF certificate of type 2, downloaded in advance from the KSeF Taxpayer Application. Here is the catch: you cannot obtain that certificate during an outage, because downloading it requires a working system. If you do not have it today, your offline procedure exists on paper only.
One exception simplifies things: if the invoice reaches the buyer outside KSeF only after it has been uploaded, a single QR code carrying the KSeF number is enough.
Step 4: what happens when the system comes back
The outage ends, and the part that is easy to sleep through begins, because nothing hurts anymore.
Upload the backlog. Offline24 gives you the next business day. Emergency mode gives you 7 business days from the day the failure ends, and if the Ministry announces another failure during that window, the clock restarts from the end of that one.
Verify that every invoice received a KSeF number. That number is the only proof the document actually landed in the system. One missing number in a batch is a classic post-outage scenario.
Flag the invoices correctly in JPK_V7. An invoice issued offline that received its KSeF number later carries its own marking in the VAT ledger and belongs to the period matching its issue date, not the upload date.
The consequence of missing a deadline is specific. Art. 106ni(1)(3) of the VAT Act provides for a penalty of up to 100% of the VAT shown on the invoice, or up to 18.7% of the total amount due where no VAT is shown. These penalty provisions become applicable from 1 January 2027, which makes 2026 the year to get the procedure right.
How this works in Biurko
The design assumption was simple: during an outage, a human should not be making technical decisions.
Biurko detects a KSeF gateway outage automatically, based on a run of failed responses within a short window, and switches new submissions into offline24 mode instead of returning an error. An invoice issued during that window gets a validated FA(3) XML file stored in the archive, its SHA-256 hash, an offline reference code, and a QR code with the verification link on the buyer's PDF.
When the system recovers, queued transmissions return to the pipeline automatically and on a cycle, with nothing to click. If one misses its deadline, the document does not disappear quietly: it moves to a review queue and the person who issued it gets notified.
To be straight about it: the second QR code ("CERTYFIKAT") requires a type 2 KSeF certificate obtained on your side. No software can arrange that for you retroactively.
Checklist: prepare this before KSeF goes down
Download a type 2 KSeF certificate from the Taxpayer Application and confirm your software can generate the "CERTYFIKAT" code from it.
Check that your system produces valid FA(3) XML without a KSeF connection. If it only produces a PDF, you do not have an offline mode.
Bookmark the announcement sources: the Ministry of Finance BIP and the technical announcements on ksef.podatki.gov.pl. Decide who checks them.
Agree in advance how invoices reach buyers outside KSeF (email, client portal, printout). This is a conversation to have before the counter, not at it.
Assign ownership of the post-outage upload. The deadline runs whether or not anyone remembers it.
Run one dry rehearsal. Cut your internet for ten minutes and issue an invoice. You will learn more than from any guide.
Summary
A KSeF outage does not stop your sales, provided you know which mode you are in and what your deadline is. The difficulty is that the decision has to be made in under a minute, in front of a client, without access to the system you would normally use to check.
Which is why the software should make that call while you just issue the invoice. Biurko detects the outage, switches modes, generates the offline code, and uploads the backlog once the system returns. Create a free account and see how your invoicing behaves when KSeF stops responding.
FAQ
What do I do if KSeF is down and I need to issue an invoice? Issue it in offline24 mode using the FA(3) structure and upload it to KSeF no later than the next business day after the issue date. You do not need to wait for any Ministry of Finance announcement, as this mode is always available.
How long do I have to upload an invoice after a KSeF outage? In offline24 mode, the next business day after the issue date. In emergency mode announced by the Ministry, 7 business days from the day the failure ends. If another failure is announced during that period, the clock runs from the end of that one.
What is the difference between offline24 and emergency mode? You choose offline24 yourself, for instance when your internet is down, and you get one business day to upload. Emergency mode applies only when the Ministry announces a failure in BIP and in the interface software, but it gives you 7 business days.
Is an offline invoice valid without a KSeF number? Yes. The issue date is the one stated on the invoice, and the KSeF number is assigned once the document is uploaded. The obligation to upload within the deadline still applies.
Why are there two QR codes on an offline invoice? The first gives access to the invoice in KSeF and verifies its data, the second confirms the issuer's identity. The second requires a type 2 KSeF certificate. Both are needed only when you hand the invoice to the buyer outside KSeF before uploading it.