Three special modes you need to know
Mandatory KSeF provides for situations where an invoice does not reach the system immediately. In practice there are three scenarios: offline24 mode, an outage announced by the Ministry of Finance, and complete system unavailability.
Offline24 mode
A taxpayer may issue an invoice outside the system (with a QR code and offline marking) and must submit it to KSeF no later than the next business day. This is useful for field sales, connectivity problems or work outside the office. Important: the invoice issue date is the date in field P_1, not the submission date.
KSeF outage
When the Ministry of Finance announces an outage, invoices are issued electronically outside KSeF and must be submitted within 7 business days after the outage ends. No sanctions apply during the outage.
Consumer invoices
Sales to private individuals (B2C) are not covered by the KSeF obligation — a consumer invoice can be issued in KSeF voluntarily or outside the system and simply delivered to the customer in the agreed form. If the customer provides a NIP and acts as a business, the invoice must go through KSeF under general rules. Make sure your sales systems distinguish these two cases correctly.
Most common problems in practice
- confusing the issue date with the submission date — this affects VAT timing and currency rates,
- no internal procedure for outages (who issues, who submits later, who tracks deadlines),
- incorrect QR codes on offline invoices handed to buyers,
- invoices with a buyer's NIP issued outside KSeF "because the client asked" — this violates the rules.
Our recommendation
Every company should have a short written emergency invoicing procedure and trained staff. At LinTax we prepare such procedures for our clients and monitor Ministry announcements on system status.