With the introduction of the National e-Invoicing System (KSeF), many businesses are asking: Do I always have to issue invoices inside KSeF?
The answer is: not always. The VAT Act identifies several situations where issuing invoices outside the system is permitted – and only later (or not at all) must they be sent to KSeF.

1. Four situations when invoices may be issued outside KSeF

Invoices issued outside KSeF are permitted when:

• using offline24 mode,
• scheduled KSeF maintenance is announced in the Ministry of Finance’s Public Information Bulletin,
• a system failure occurs,
• a failure is announced through mass media (e.g., TV, radio).

Each scenario imposes different obligations, deadlines for sending invoices to KSeF, and rules for determining the invoice issuance and receipt dates.

2. Offline24 Mode – invoice first in your system, then in KSeF

Offline24 is designed to support businesses in everyday operations – it can be used by anyone, without special conditions.

How does it work?

• You issue the invoice in your own system (electronically, using the official KSeF schema).
• The invoice becomes a valid legal document immediately – you can send it to your client (e.g., PDF by email).
• You must send it to KSeF no later than the next business day so it can receive a KSeF number.
• If a system failure is announced during that time, the deadline is extended to 7 business days after the failure ends.
• If a failure is announced via mass media, there is no obligation to send the invoice to KSeF afterwards.
• Starting in 2027, failing to submit invoices on time may result in financial penalties.

Why are there two QR codes?

Invoices issued in offline24 mode – before they are sent to KSeF – must include:

• a QR code identifying the invoice,
• a second QR code generated based on the KSeF certificate.

These allow the buyer to verify the invoice’s authenticity and accuracy.

Once the invoice is submitted to KSeF and receives a number, only one QR code (the identifying one) needs to appear on the visualization.

Issuance and receipt dates – crucial for VAT

Issuance date:

This is the date entered in field P1 (the date you put on the invoice).
It will also appear in the KSeF number and in the confirmation (UPO).
This is an exception to the usual rule that “date of submission to KSeF = issuance date.”

Receipt date:

Generally, this is the date the KSeF number is assigned.
For some taxpayers defined in the Act, it may be the actual date of receiving the invoice outside KSeF, if that delivery method was agreed.

The buyer must ensure:

• correct recognition of the receipt date in VAT records,
• avoiding double posting – once from the outside-KSeF invoice and again when it appears in the system.

3. Scheduled KSeF maintenance – the “classic” offline mode

KSeF maintenance:

• is scheduled in advance,
• usually happens at night,
• is announced in the Ministry of Finance’s Public Information Bulletin (BIP MF).

During maintenance:

• invoices cannot be issued inside KSeF,
• the offline mode (similar to offline24) may be used.

What does this mean?

• You issue the invoice outside KSeF, using the required schema.
• You add the necessary QR codes.
• You deliver the invoice to the buyer in the agreed manner (e.g., email).
• You must send the invoice to KSeF no later than the next business day after maintenance ends.

Issuance and receipt dates follow the same rules as in offline24 mode.

4. System failure – what then?

When an unexpected technical failure occurs, KSeF will publish:

• the start and end time of the failure,
• the period during which the system was unavailable.

An automated interface will also notify connected accounting systems.

During a failure:

• You may issue invoices outside KSeF.
• They must follow the KSeF schema and be electronic.
• They may be delivered to the buyer in PDF (if agreed).
• They must include a QR code.

After the failure ends:

• You have 7 business days to send those invoices to KSeF.
• Missing this deadline may lead to penalties from 2027.

Issuance date: P1 date.
Receipt date: actual receipt date unless a KSeF number is assigned earlier.

You may also issue corrective invoices – but only for invoices already assigned a KSeF number.
You cannot correct an invoice that has not yet been submitted to KSeF.

5. Failure announced in mass media – extraordinary situations

For unexpected, large-scale disruptions (e.g., serious infrastructure risks), the VAT Act allows a special procedure:

• The system failure may be announced via mass media, not just in BIP MF.
• Taxpayers may issue invoices and corrective invoices in any form – paper or electronic.
• There is no obligation to later send these invoices to KSeF.

This option is reserved only for exceptional cases.

6. What should businesses do now?

To ensure smooth operations under KSeF – both in standard and emergency modes – companies should:

• create an internal emergency invoicing procedure,
• establish clear deadlines and responsibilities for sending invoices to KSeF,
• ensure correct QR code generation,
• implement controls to avoid duplicate postings,
• train accounting and sales teams to understand the differences between online mode, offline24, system failures, and maintenance.

Note: This material is for informational purposes and does not constitute legal advice. Consult a tax advisor for specific cases.

Not sure how to handle offline24, system failures or KSeF maintenance correctly? Easybooks helps businesses set up compliant invoicing processes – get in touch!