How do I correct an invoice already filed in KSeF?

You issue a correction invoice (KOR) as a new structured FA(3) document that references the original invoice's KSeF number. You don't edit the original — the correction is a separate document with its own KSeF number and UPO.

Can I cancel a faulty invoice in KSeF?

An invoice that already has a KSeF number can't be cancelled or withdrawn. Cancellation is only possible before the system assigns a number — while the invoice is still "sent", "processing" or "rejected". Once it has a number, a correction invoice is the only route.

What about correcting a sale made through Stripe?

A Stripe credit note maps to a correction. A good tool turns it into an FA(3) KOR that references the original invoice's KSeF number and files it automatically.

KSeF Correction Invoice (KOR): How to Fix a Structured Invoice

An invoice that already has a KSeF number can't be cancelled — you issue a correction invoice in the FA(3) structure that references the original's KSeF number, states the reason and the corrected amounts, and gets its own new KSeF number and UPO. That is the only route, full stop.

You fix a mistake, return or discount only through a correction invoice (KOR) — a separate FA(3) document that references the KSeF number of the original. The system keeps a complete, immutable history.

You can only cancel before KSeF assigns a number

Cancellation is only possible before the system assigns a KSeF number — while the invoice has the status "sent", "processing" or "rejected". In that window the document isn't yet a structured invoice. Once KSeF assigns a number and issues a UPO (the official confirmation of receipt), the door closes: a correction is all that's left.

Why you can't "edit" an invoice

An invoice in KSeF has a number and a UPO — it's proof that it was issued at a specific moment. If you could change it, that proof would be worthless. So every change is a new correction document.

How do you correct an invoice in KSeF?

You issue a correction invoice (KOR) as a new FA(3) document that points to the KSeF number of the original invoice, states the reason and the corrected amounts, and — once sent — gets its own new KSeF number and UPO. You don't edit or cancel the original.

From 1 February 2026 you issue corrections in the FA(3) structure — even when the original invoice was an FA(2) or FA(1).

Create a new FA(3) document of type correction and point to the KSeF number of the original invoice.
Give the correction date and number and the party details (seller, buyer).
Enter the number and date of the original invoice, the reason for the correction, and the scope of the changes.
Give the corrected net, VAT and gross amounts (these fields come from art. 106j of the VAT Act). A correction can be positive or negative.
Send it to KSeF — the correction gets its own new KSeF number and UPO.

Common scenarios

Goods returned / service cancelled — a downward correction.
Post-transaction discount — a downward correction.
Wrong price or VAT rate — a correction that fixes the data.

Corrections and Stripe

In Stripe, the equivalent of a correction is a credit note. KSeF Kit turns it into an FA(3) KOR that automatically references the original invoice's KSeF number — you don't have to retype identifiers by hand. That removes the most common correction mistake: linking to the wrong original.

Common mistakes

No reference to the original's KSeF number — the correction "hangs in mid-air".
No reason for the correction — it's a required field under art. 106j; without it the document is incomplete.
Trying to cancel an invoice that already has a KSeF number — once a number is assigned, that route is gone.
Re-sending a fixed invoice instead of a correction — those are two different documents.
Calculating the differences by hand — it's easy to slip; better to let a tool do it.