KSeF Offline Mode Explained: What It Is and How to Use It

KSeF — Poland's national e-invoicing platform — is a government infrastructure system. Like all infrastructure systems, it has scheduled maintenance windows and occasional unplanned outages. During these periods, you cannot submit invoices to KSeF in real time.

So what do you do? The answer is KSeF offline mode (tryb offline) — a specific procedure that allows you to issue invoices during KSeF unavailability and submit them within a defined window afterwards.

What Is KSeF Offline Mode?

KSeF offline mode is a legally defined procedure allowing businesses to:

Issue FA_VAT XML invoices during periods when KSeF is unavailable
Assign a temporary invoice number without waiting for a KSeF reference number
Submit the offline invoices to KSeF within 72 hours of KSeF coming back online

The offline invoices are legally valid from the moment they're issued, even without a KSeF reference number — provided they are submitted within the 72-hour window.

When Does Offline Mode Apply?

Offline mode applies during any period of KSeF unavailability — meaning the KSeF API is not accepting submissions. This includes:

Scheduled maintenance windows

The Ministry of Finance announces scheduled maintenance in advance (typically on the KSeF portal and gov.pl/ksef). Maintenance windows are typically:

Sunday nights, approximately 22:00–02:00 CET
Quarterly extended maintenance (announced at least 2 weeks in advance)

Unplanned outages

Rare but possible technical failures. The Ministry of Finance monitors KSeF availability 24/7. If KSeF is unavailable for more than 4 hours, an official "offline period" is declared.

During routine scheduled maintenance (typically 4–6 hours on Sunday night): Most businesses simply don't issue invoices during this window. The 72-hour post-restoration submission window typically isn't needed for Sunday-night maintenance.

During a longer unplanned outage or extended maintenance: Offline mode becomes essential, especially for businesses that invoice continuously (e.g., high-volume distributors, utilities).

How Offline Mode Works: Step by Step

Phase 1: Recognise that KSeF is unavailable

Your accounting software will typically alert you when KSeF is unavailable (error on submission attempt). You can also check:

The official KSeF status page
Ministry of Finance social media channels
Your KSeF intermediary's status notifications

Phase 2: Switch to offline invoice generation

In offline mode, you generate FA_VAT XML invoices normally in your accounting software — but instead of submitting them to KSeF for a reference number, you:

Assign the invoice your own sequential invoice number (following your normal numbering series)
Do not include a KSeF reference number in the XML (there isn't one yet)
Mark the invoice as offline — most accounting software has a specific field or status for this
Issue the invoice to your customer (you can send it to them without the KSeF number)

Phase 3: Inform your customer of the offline invoice

If you send the invoice to a customer before it has a KSeF reference number, you must inform them that it is an offline invoice issued during KSeF unavailability. Most accounting software includes a note on the invoice PDF to this effect.

Customers should not refuse offline invoices — they are legally valid as long as they're submitted to KSeF within the 72-hour window.

Phase 4: Submit the offline invoices when KSeF comes back online

When KSeF is restored, submit your batch of offline invoices within 72 hours of restoration.

Your accounting software should have a "submit offline invoices" or "sync offline invoices" function. This submits all pending offline invoices to KSeF in batch and retrieves the KSeF reference numbers.

The 72-hour clock starts from when KSeF comes back online, not from when you issued the invoice. If you issued an invoice at 10:00 on Sunday during a maintenance window and KSeF came back at 02:00 on Monday, you have until 02:00 on Thursday to submit.

Phase 5: Update invoices with KSeF reference numbers

Once submitted, KSeF assigns reference numbers to your offline invoices. Your accounting software should:

Update each invoice record with the KSeF reference number
Send updated invoice copies to customers if required
Reconcile the KSeF numbers with your accounting records

The 72-Hour Rule: What Happens If You Miss It?

If you do not submit offline invoices within 72 hours of KSeF restoration, those invoices are considered non-compliant. The invoices themselves are valid for accounting purposes, but:

They do not have a KSeF reference number
They cannot legally be "corrected" to compliant status
They are subject to penalty (typically PLN 100–500 per non-compliant invoice in practice)
You may need to reissue with a new invoice number and submit to KSeF normally

In practice: Set up automatic alerts in your accounting software for pending offline invoices. Most accounting platforms (Comarch, INSERT nexo, enova365) have a dashboard showing offline invoices awaiting submission.

Testing Offline Mode Before You Need It

The Ministry of Finance's KSeF test environment (ksef-test.mf.gov.pl) supports offline mode simulation. You can:

Generate offline invoices in the test environment
Simulate a KSeF restoration
Submit the test offline invoices and receive test KSeF reference numbers

Strongly recommended: Test your offline mode procedure at least once before your first live outage. Companies that had drilled their offline procedure found the February 2026 maintenance window straightforward; companies that hadn't were scrambling.

Software Settings for Offline Mode

Comarch ERP Optima

Settings → KSeF → Tryb awaryjny (Emergency mode). Enable to allow offline invoice generation. Check "Automatyczna synchronizacja" to auto-submit when KSeF is restored.

INSERT nexo

KSeF configuration → Offline mode → Enable. The built-in offline mode was one of INSERT nexo's advertised features for the 2026 mandate.

enova365

Administration → KSeF integration → Offline mode settings. Configure the 72-hour submission reminder.

Sage Symfonia

KSeF module → Configuration → Offline invoice handling. Sage Symfonia includes automated token rotation and automatic offline invoice queuing.

wFirma / iFirma

Both platforms include offline mode as a standard feature. When KSeF is unavailable, the invoice is held in a pending queue and submitted automatically when connectivity is restored.

Offline Mode vs. Simplified Invoices

Offline mode is specifically for periods of KSeF unavailability. It is not a workaround for:

Invoices you don't want to submit to KSeF (all domestic B2B invoices must go through KSeF)
Invoices with errors you haven't fixed
Cross-border invoices (which are outside KSeF scope regardless)

Do not confuse offline mode with invoices that are simply not yet sent — all submitted invoices must go through KSeF on the normal live path unless KSeF is formally unavailable.

What About VAT Deductibility for Buyers During KSeF Outages?

Under Polish VAT law, a buyer can deduct input VAT on invoices received during KSeF unavailability periods, provided:

The invoice was issued by the seller during a formally declared KSeF unavailability period
The invoice was submitted to KSeF within 72 hours of restoration
The invoice number is traceable in KSeF after submission

If you receive an invoice from a supplier noting "offline mode," it is fully VAT-deductible once the supplier has submitted it to KSeF and the KSeF reference number has been assigned.

Summary

Question	Answer
Can I issue invoices when KSeF is down?	✅ Yes, using offline mode
How long do I have to submit to KSeF after it's restored?	⏰ 72 hours
Are offline invoices legally valid?	✅ Yes, if submitted within 72 hours
Does my customer need to know the invoice is offline?	✅ Yes — mark it clearly
Can I avoid offline mode entirely?	🔶 Mostly yes — plan invoicing around maintenance windows
What if I miss the 72-hour window?	❌ Invoice is non-compliant — penalty risk