The call comes at 4:40 pm: "this invoice is overstated, we are not paying it." A year ago that conversation ended quickly. You cancelled the document, issued a new one, and the matter stayed between two companies.
Today the invoice already carries a KSeF number, sits in your client's accounting system, and its receipt date was assigned automatically the moment that number was granted. The dispute is now a tax document on both sides, running on a schedule that does not wait for your negotiation. For foreign-owned companies with Polish entities, this is often the first place where Polish e-invoicing rules become tangible rather than theoretical.
Here is how to identify what kind of correction the situation needs, how to issue it, when it lands in your VAT return, and what to send the client.
Why invoice disputes work differently now
Three changes reshaped the conversation.
There is no reject button in KSeF. A client who disagrees with an invoice receives it anyway. The Ministry of Finance states plainly that the system does not allow editing, cancelling or deleting an issued invoice, and that errors are fixed exclusively through a correction invoice (KSeF 2.0 Q&A).
The buyer-side correction note is gone. With Article 106k repealed, a buyer cannot fix even a typo in their own company name. They report the error and wait for you.
Delivery is now a hard, documented fact. A structured invoice is deemed received on the day its KSeF number is assigned (Article 106na(3) of the VAT Act). Arguments about spam folders are over.
The practical consequence for a seller: you are the only party who can solve your client's problem, which makes correction speed part of customer service rather than a back-office chore.
First thirty minutes: name the actual problem
Before opening any system, classify the dispute. Five common situations call for five different responses.
What the client disputes What you issue Note Typo in company name, address, item description Correction of formal data, amounts unchanged The buyer cannot fix this themselves Wrong quantity, wrong price, item billed twice Downward or upward correction Cause: original error Discount, return, price cut agreed later Downward correction Cause: new event Invoice issued to the wrong company or tax ID Zero-out correction plus a new invoice Ministry of Finance position Client says the invoice never arrived No correction needed Check the KSeF number and UPO receipt
That last row matters more than it looks. A large share of "complaints" are not substantive disputes at all, just documents stuck somewhere in the client's approval flow. Check the document history first. In Biurko every invoice carries an activity log showing when it was issued, when KSeF accepted it, when it was emailed and when the client opened it. One screenshot usually ends the discussion.
Issuing a correction in KSeF, step by step
Open the original invoice and create the correction from it, rather than building a new document from scratch. The correction must reference the original invoice number and its KSeF number, and that field is easy to mistype manually.
Choose the correction type. The FA(3) schema requires a
TypKorektyvalue: correction due to an error, correction due to a new event, or a mixed correction. This drives which period the document affects.Write the reason for the correction. It is mandatory and your client will read it. "Quantity adjusted per acceptance protocol of 12 Aug 2026" reads very differently from "correction".
Restate the lines as before and after values. A correction does not replace the original invoice, it expresses the delta. In Biurko the lines are copied from the original with the before state prefilled, so you only touch what actually changed.
Send it to KSeF and keep the UPO. Until the document has a KSeF number it does not exist for tax purposes. A rejected XML file is not a correction, it is a file.
The wrong-tax-ID case follows its own path. The Ministry's guidance is to zero out the invoice issued to the wrong buyer and then issue a fresh invoice with the correct NIP. Correcting only the tax ID number is not the accepted route. In Biurko the zero-out is a single action on the original invoice, with no manual line editing.
When the correction hits your VAT return
This is the part worth explaining to your client, because it works in their favour too.
For a downward correction issued online, the seller reduces the taxable base and output VAT in the period the correction was sent to KSeF. No confirmation of receipt is needed, because making the document available in the system replaces the old proof of delivery (Article 29a(13) and (14) of the VAT Act as amended from 1 February 2026).
On the buyer side, Article 86(19a) mirrors this: input VAT is reduced in the period the correction was received, which in practice means the period the KSeF number was assigned.
For documents issued in offline24 mode or during a KSeF outage, the decisive moment is the assignment of the KSeF number after the document is uploaded, not the offline issue date. If the correction was created entirely outside KSeF, the simplification does not apply and the old proof-of-receipt rules return. The Ministry covers the detail in the KSeF 2.0 handbook.
Upward corrections follow the familiar logic: an original error reaches back to the period of the original invoice, a new event is recognised currently.
What to write to the client
Short, specific, no apologising in circles. A template that works:
Hello, confirming your query on invoice FV/2026/08/114. You are right, line 3 was billed at the wrong quantity. The correction has been issued and sent to KSeF (correction number KOR/2026/08/27). The remaining balance is PLN 4,305.00 and the due date is unchanged. Happy to answer anything else here.
Four things this does well: it confirms the problem, gives a document number, gives the new amount, and asks the client to do nothing. There is no acceptance step for corrections in KSeF, so do not invent one.
If you disagree with the claim, do not issue a correction "just to keep the peace". Explain why the invoice is right and offer a call. A correction issued under pressure and then reversed by another document looks worse than one difficult conversation.
Three mistakes that damage the relationship more than the error did
Promising to cancel. "I will cancel this invoice and issue a new one" is a promise you can no longer keep. The client hears cancellation and then sees two documents in KSeF. Talk about corrections from the first message.
Correcting a correction. When the correction itself is wrong, the right move is another correction against the original invoice, not against the correcting document. Biurko blocks correction-on-correction and points you to the document to open.
Internal "correction notes". A document with that name no longer has a legal basis. An internal memo or an error report is fine, but naming it after a repealed instrument confuses accounting on both sides.
Checklist when a client pushes back
Read the document log before assuming the invoice content is the problem.
Classify the dispute: formal data, amount, new event, wrong buyer.
Decide whether it is a downward, upward or zero-out correction.
Build the correction from the original so the KSeF number links automatically.
Write the reason in language your client understands.
Send to KSeF and confirm the UPO before replying.
Give the correction number, the new amount and the payment date in one message.
Wrapping up
A KSeF invoice correction is technically simpler than the old paper trail of delivery confirmations, but it leaves a permanent record and demands a different conversation. The seller who wins is the one who responds the same day, names things accurately, and never promises an operation the system does not perform.
In Biurko you create a correction from the original invoice in a few clicks, with the KSeF number linked automatically, the before and after states prefilled, and plain-language messages when KSeF rejects something. Create a free account and run a full correction on the test environment before you do it with a real client watching.
FAQ
Can a client reject an invoice in KSeF? No. The system has no rejection mechanism for buyers. A client can report an error to the seller, and the seller decides whether to issue a correction invoice. Until then the invoice remains in circulation with its assigned KSeF number.
Can I cancel an invoice already sent to KSeF? No. Once accepted, an invoice cannot be edited, cancelled or deleted. A zero-out correction achieves a similar economic result, but both documents stay in KSeF permanently.
Do buyer-side correction notes still exist in Poland? No. Article 106k of the VAT Act was repealed on 1 February 2026. A buyer can no longer fix even formal details on a received invoice and must ask the seller to issue a correction invoice.
When do I account for a downward correction? For a structured correction issued online, in the period it was sent to KSeF, with no proof of receipt from the buyer. In offline modes, the date the KSeF number is assigned after upload is decisive.
What if the invoice went to the wrong tax ID? Issue a zero-out correction against the invoice carrying the wrong NIP, then issue a new invoice to the correct buyer. The Ministry of Finance indicates that correcting only the tax ID is not the right approach.