The National e-Invoicing System (KSeF) is now mandatory for the vast majority of businesses in Poland, and the transition period during which the tax authorities refrained from penalising errors has come to an end. In practice, most questions from our clients concern not sales invoices themselves but corrections: how to issue them, what to do about a mistake in the buyer's details and in which month a correction should be included in the VAT return. This article sets out the rules that apply now that the structured invoice has become the standard.
Corrections always in KSeF, always with the original KSeF number
A correction invoice to an invoice issued in KSeF must also be issued in KSeF. The key element is the KSeF identification number of the original invoice, the 35-character identifier assigned by the system. Without it the correction is not linked to the original document and the system may reject it. Otherwise the correction contains the same elements as before: the issue date, a sequential number, the reason for the correction and the corrected data or the correction amount.
The situation is different when correcting an invoice that was issued outside KSeF, for example in 2025. Such a correction is also issued in KSeF, but instead of the original invoice's KSeF number, only its own invoice number is indicated, because the original document never entered the system.
The end of correction notes
Correction notes (noty korygujące) cannot be issued for structured invoices. If a buyer spots an error in their own details, such as a typo in the company name or a wrong address, they can no longer fix it themselves with a note, as was done for years. The only route is to ask the seller to issue a correction invoice in KSeF. Keep this in mind when checking purchase invoices: an error in the buyer's tax ID means the invoice will not reach the right entity in the system at all, so it has to be corrected to zero and reissued.
Downward corrections on the seller's side
The biggest change compared with previous years is the simplification of corrections that reduce the tax base. The seller reduces the base and output VAT in the period in which the correction was issued in KSeF. There is no longer any need to collect documentation confirming that the terms of the correction were agreed with the buyer, such as email correspondence or annexes. The issue date confirmed by the system is sufficient evidence.
Note one exception: if the correction was issued outside KSeF, for example in emergency or offline mode, and reached the system later, the settlement period is determined by the date the buyer received the correction, as under the general rules.
Downward corrections on the buyer's side
The buyer reduces input VAT in the period in which the correction invoice was received in KSeF, i.e. the month in which the system assigned its number. It does not matter when the buyer logged in or downloaded the document. This is why it makes sense to set up regular, at least weekly, downloads of invoices from KSeF, so that corrections do not slip into the following month and force an amended JPK_V7M return.
Upward corrections
The rules for corrections that increase the tax base have not changed and still depend on the reason for the correction:
- Original cause (the error existed when the invoice was issued, e.g. a wrong price or VAT rate): the correction is recognised retroactively, in the period of the original invoice, which means an amended return and possible interest.
- Subsequent cause (new circumstances after the sale, e.g. a price increase agreed later): the correction is settled on an ongoing basis, in the period it was issued.
For this reason the "reason for correction" field in KSeF is more than a formality. A precise description makes it easier to defend current-period treatment during an audit.
Collective corrections and corrections to zero
KSeF supports collective corrections covering multiple invoices for a single buyer, for example an annual rebate. Such a correction lists the KSeF numbers of all corrected invoices. A correction to zero is also possible and replaces the former practice of cancelling an invoice: in KSeF a document accepted by the system cannot be deleted or cancelled, so an erroneous invoice is always corrected to zero.
The most common mistakes we see in practice
- Issuing a correction in accounting software without sending it to KSeF, assuming that emailing it is enough.
- Omitting the KSeF number of the original invoice, or entering the invoice's own number instead of the system identifier.
- Recognising a downward correction on the buyer's side in the month it was booked rather than the month it was received in KSeF.
- Trying to fix buyer details with a correction note.
- Issuing a new invoice without first correcting the erroneous one to zero, which doubles revenue and output VAT.
How it works for LinTax clients
Our clients see the KSeF status of every invoice and correction directly in the LinTax Cloud portal, and we download purchase invoices from the system on an ongoing basis, so corrections land in the right period without any extra action on the client's side. If you are unsure about a specific correction, message us through the portal or contact the office.