Error codes · KSeF · Poland
KSEF-003Partly
Invoice number sequence gap in Poland
This is the rejection, word for word: „[KSEF-003] Invoice numbers must be sequential without gaps within each calendar year. KSeF rejects invoices with numbering gaps or duplicates.“
Why this matters in Poland
Poland requires e-invoicing using KSeF XML format. An invoice with this error is rejected; it cannot be processed under Poland's rules.
What to have readyThe correct figures from your bookkeeping; we show you which field is affected.
What we doEnsure continuous sequential numbering per year.
How to fix KSEF-003
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Poland e-invoicing requirements
| Phase | Status | Scope |
|---|---|---|
| KSeF voluntary | Live (Jan 2022) | All VAT payers (opt-in) |
| B2B mandatory — Phase 1 | Live (Feb 1, 2026) | Large taxpayers (>200M PLN turnover) |
| B2B mandatory — Phase 2 | Live (Apr 1, 2026) | All remaining VAT-registered entities (SMEs, sole proprietors, VAT-exempt businesses) |
| B2G | Live (Feb 1, 2026) | Included in general KSeF mandate |
| Financial penalties | Jan 1, 2027 | Up to 100% of VAT amount on non-compliant invoices |
Known causes
Multiple systems using same number series
Cancelled invoices leaving gaps
Database restore issues