KSeF Is Down: What to Do and by When to Send the Invoice

When KSeF is down you keep issuing invoices, just outside the system. You do not lose the right to sell, but you do not get an open-ended extension either. The base rule: an invoice issued offline must be sent to KSeF "niezwłocznie, nie później niż w następnym dniu roboczym po dniu jej wystawienia" — immediately, no later than the next business day after the day it was issued (art. 106nda ust. 2 of the VAT Act). There is exactly one exception, and you have to be able to recognise it: during a declared KSeF outage the deadline is 7 business days from the day the outage ends (art. 106nf).

How much time you have depends on what exactly broke, and who announced it. The rules distinguish four modes and each carries a different deadline. The common mistake looks like this: someone sees a connection error, says "KSeF outage" and assumes they have a week. Usually they have one business day.

First, work out which situation you are in

The rest of this article walks through each row in turn.

Offline24 mode: the rule you will use most often

Offline24 comes from art. 106nda of the VAT Act and is voluntary. You need no announcement and no permission: you decide whether to issue the invoice online or outside the system. That is why offline24 is the answer to everything the Ministry of Finance has not announced — your internet died, your server died, you are invoicing in the field, KSeF returns an error and no announcement exists.

An offline24 invoice is still a structured invoice. It is created to the FA schema published under art. 106gb; it simply reaches the buyer before it has a KSeF number. The obligation is short and plain. The taxpayer "jest obowiązany niezwłocznie, nie później niż w następnym dniu roboczym po dniu jej wystawienia, przesłać tę fakturę do Krajowego Systemu e-Faktur" (art. 106nda ust. 2). The biznes.gov.pl portal puts it the same way — "najpóźniej następnego dnia roboczego po dniu wystawienia przesłać fakturę do KSeF" — and gives an example: an invoice dated 5 May goes out by 6 May at the latest.

Two things people get wrong:

• It counts business days, not hours. The name "offline24" suggests 24 hours; the statute says the next business day. A Friday invoice has until Monday, and if Monday is a public holiday, until Tuesday.
• The clock starts on the day of issue, not at the end of the outage. This is what separates offline24 from the other modes. If KSeF stays down for three days and you issue invoices each day, every one of them has its own deadline, already blown. In the MF-declared modes the clock only starts once the interruption ends.

KSeF unavailability: announced maintenance

When the Ministry of Finance plans maintenance, it publishes an unavailability period in the Public Information Bulletin and in the interface software (art. 106ne ust. 4). During that window you issue invoices offline under art. 106nh, and you count the deadline differently: you send the invoice to KSeF "nie później niż w następnym dniu roboczym po zakończeniu okresu niedostępności" — no later than the next business day after the unavailability period ends.

The difference from offline24 is practical. A maintenance window from Friday evening to Saturday morning gives every invoice issued inside it one shared deadline, rather than a separate deadline each. The condition is strict, though: the announcement has to exist. Without a declared unavailability period you are back in offline24, with the shorter deadline.

KSeF outage: 7 business days, but only with a BIP announcement

An outage is unplanned. The Minister of Finance publishes a BIP announcement that an outage has started, then a second one that it has ended (art. 106ne ust. 1). Only that first announcement opens the art. 106nf regime, in which you issue electronic invoices to the schema and have "7 dni roboczych od dnia zakończenia awarii Krajowego Systemu e-Faktur" — 7 business days from the day the outage ends — to send them to the system.

Two details worth remembering:

• If an announcement of another outage appears within those seven days, you count the deadline from the day that later outage ends. It does not lapse; it restarts.
• No announcement, no emergency regime. The mere fact that your software cannot reach KSeF does not start the seven-day clock. Legally you are in offline24.

So the first thing to do after a failed submission is not to retry in a loop, but to check whether an announcement exists. That decides whether you have one day or a week.

Total outage: paper, and nothing to catch up on

There is one extreme case: an outage severe enough that the Ministry cannot publish an announcement in the BIP at all. Then "minister właściwy do spraw finansów publicznych zamieszcza w środkach społecznego przekazu komunikat o wystąpieniu awarii" (art. 106ne ust. 3), and you apply art. 106ng: "w okresie trwania awarii wystawia faktury w postaci papierowej lub faktury elektroniczne" — during the outage you issue paper invoices or ordinary electronic invoices.

This is the only mode where you do not have to stay with the FA schema. A plain PDF or paper will do. More importantly, as biznes.gov.pl states: "Takich faktur nie wysyłasz do KSeF po ustaniu awarii, ani nie oznaczasz ich kodami" — you never send those invoices to KSeF once the outage is over, and you do not mark them with codes. No catching up, no QR codes, no deadline. This mode is the rarest and is routinely confused with an ordinary outage, which works exactly the other way round.

Date of issue vs date of submission: the most common mix-up

In online mode the two dates are one and the same: a structured invoice is deemed issued on the day it is sent to KSeF (art. 106na ust. 1). Until you send it, the invoice formally does not exist. See what the UPO is — it is the UPO that carries the timestamp of that event.

In offline mode that relationship comes apart, and this is the heart of the matter. The date of issue is the one "o której mowa w art. 106e ust. 1 pkt 1, wskazaną przez podatnika" (art. 106nda ust. 10) — the date the taxpayer puts on the invoice. The same holds during unavailability and during an outage: the date of issue is the date shown on the document.

Three consequences follow:

1. Sending late does not move the date of issue. An invoice dated 3 August and sent on 6 August is still an invoice dated 3 August, with everything that implies for the tax point and the settlement period. You breach the submission deadline, not the document's date.
2. The KSeF number arrives after the invoice does. The buyer receives a document with no number, and the number is assigned only once you send it. The copy you already handed over does not stop being valid.
3. In online mode an outage creates no backlog. Since the invoice is issued only at the moment of submission, KSeF going quiet does not leave you with an overdue invoice — it leaves you with an invoice not yet issued. The clock that runs then is the general deadline in art. 106i ust. 1: by the 15th day of the month following the month of supply. Only the decision to issue offline starts the short art. 106nda clock.

What the buyer's copy must show

An invoice issued offline, in offline24, or during a declared unavailability or outage and handed to the buyer outside the system must carry two QR codes: KOD I labelled "OFFLINE" and KOD II labelled "CERTIFICATE". That comes from art. 106nda ust. 6, and KOD II requires a certificate you download from KSeF (art. 106nda ust. 7), which confirms the issuer's identity.

We cover the mechanics of both codes, their contents and how they are computed separately, in QR codes on a KSeF invoice. For outage purposes only one thing matters here: get the certificate in advance. You cannot download it mid-outage from a system that is down, so if you ever plan to issue offline, sort the certificate out while KSeF is running normally. For the difference between a certificate and a token, see token or certificate. The one exception is a total outage: there you add no codes at all.

How to tell whether KSeF is really down

The honest answer: the Ministry of Finance publishes no live status page. There is no green dot to refresh. There are two official channels, and only they carry legal effect:

• The Ministry of Finance Public Information Bulletin (BIP). Announcements that an outage has started or ended, and information about unavailability periods, go there. Only a BIP announcement opens the art. 106nf or art. 106nh regime.
• Technical announcements on ksef.podatki.gov.pl. An archive of notices about maintenance, API limits and environment changes. An example from this year: the announcements of 5 and 11 May 2026 about a planned break, then disruption, then restored access to Profil Zaufany services. Cutting you off from KSeF does not require KSeF itself to fail. It is enough for the authentication route to stop working.

Independent uptime monitors run by third parties also exist. They are often faster than the BIP and are useful for a first diagnosis, but they are not evidence. A screenshot from a monitoring service will not earn you the seven-day deadline. The MF announcement is what counts.

A practical order of operations when a submission fails: check the BIP and the technical announcements, check that the problem is not on your side (authentication, certificate, network), and if there is no announcement, assume you are in offline24 and keep to the shorter deadline. Better to send too early than to award yourself a week you do not have.

What happens to your queue in KSeF Kit

Only what our code actually does.

KSeF Kit files invoices online only. We do not issue invoices in offline or offline24 mode and we do not generate KOD II. If you want to use offline24, you need a tool that issues the invoice outside the system and applies both codes. With us, a Stripe invoice waits until KSeF accepts it.

What happens while KSeF is not answering:

• Nothing is lost and nothing goes out twice. Every filing attempt is a separate record, so the history is auditable and a double filing is impossible.
• Transient errors are retried automatically. When KSeF answers with a server error or a rate limit, the filing job retries five times with a growing back-off.
• An invoice already sent keeps being polled. If the document reached KSeF and only the status check broke, we do not send it again. A separate job asks for the outcome every few minutes until it knows.
• An invoice that never went out stays in the queue. You see it as "Queued", and a recurring job comes back to the backlog and tries again once the system returns.
• A filing interrupted halfway becomes a manual decision. If after an hour we still cannot tell whether the invoice reached KSeF, we mark it blocked and ask you to check in KSeF whether it is already there before refiling. That is deliberate: an automatic retry here risks a duplicate.
• We show no "KSeF is down" banner. We run no availability monitoring of our own, so we do not pretend to. You see status per invoice.

For the whole path from Stripe to KSeF, see the Stripe and KSeF integration.

Penalties: where things stand today

The KSeF obligation has applied since 1 February 2026 for the largest taxpayers and since 1 April 2026 for everyone else — more on that in mandatory KSeF from 2026. Penalties for breaches are due to start on 1 January 2027. The Ministry of Finance has floated extending the penalty-free window but, as of 20 August 2026, has published no decision. Treat the date as binding and do not build a process on the assumption that it will move.

The procedure in five steps

1. Check for an announcement. The Ministry of Finance BIP and the technical announcements on ksef.podatki.gov.pl. They decide which mode you are in.
2. Issue the invoice outside the system. FA schema and two QR codes, unless a total outage has been declared — then paper or PDF.
3. Put the date of issue on the document. That is the date of issue, not the date you send it later.
4. Deliver the invoice to the buyer through an agreed channel, since KSeF cannot deliver it.
5. Send it to KSeF within the deadline. Next business day for offline24, next business day after the unavailability period ends, 7 business days after a declared outage ends. Once accepted, collect the KSeF number and the UPO.

If you take one sentence away from all this: without a Ministry of Finance announcement you have one business day, not a week.