Error codes · KSeF 2.0 · Poland
KSeF UPO (Urzędowe Poświadczenie Odbioru) not found in Poland
This is the rejection, word for word: „[KSEF-21178] You requested the UPO (Urzędowe Poświadczenie Odbioru — the official acceptance confirmation) for a KSeF invoice, but the system could not find a UPO matching the provided criteria. Either the invoice has not yet been assigned a UPO, or the search parameters (referenceNumber, KSeF number, sessionReferenceNumber) do not identify a valid invoice.“
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.
The UPO is the legal proof of receipt for a KSeF invoice — the Polish equivalent of a Peppol MLR. Downstream systems (accounting, archiving, dispute handling) rely on the UPO to confirm the invoice is officially in circulation. A UPO not-found error blocks that entire downstream chain.
How to fix KSEF-21178
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 |