CHECK-KSEF-NUMBER-MISMATCH
InvoiceIn checks · validation rule
InvoiceIn checksWarning
The KSeF number is well formed but does not agree with the invoice it arrived with: either it opens with a NIP that appears nowhere on the document, or it says KSeF accepted the invoice before the invoice was issued. The usual cause is a number taken from the wrong row of a KSeF query — which would send the payment out under another document's reference and leave the seller unable to match it. Check two exceptions before treating it as an error: the number carries the buyer's NIP under self-billing, and the NIP of a bailiff or enforcement authority, a tax representative, or a subordinate local government unit or VAT-group member when one of those issues the invoice for someone else — there the NIP is expected to differ from the seller's. A number dated before the issue date has no such exception: an invoice issued offline gets its number when it reaches KSeF, which is never earlier.
- Field
payment.ksef_number (PL national, not an EN 16931 term)- Rule set
- InvoiceIn checks
- Who has to fix it
- The receiver
This one is on the receiving side: the document itself is fine, but something the payment run needs is missing or does not match — it is fixed in your own integration, not by the supplier.
Check your own invoice
Drop the file that failed. We parse it, run the official rule sets against it and list every finding with a fix — 20 invoices per day, no key, nothing stored.
Open the live demoSame explanation over the API: GET /v1/rules/CHECK-KSEF-NUMBER-MISMATCH?lang=en