Does KSeF 21401 mean my invoice was rejected?

Yes. 21401 is returned before the invoice enters the system, so it has no KSeF reference number and no legal effect. You do not need a correction invoice — fix the XML and resubmit as a fresh document.

Can Invoice Navigator auto-fix KSEF-21401?

Partially. Structural issues (element order, namespace, decimal formatting, whitespace) are auto-fixed. Missing required business data (invoice number, amounts, buyer NIP) requires input from your ERP because the fields are not present at all.

Why did the same file pass yesterday and fail today?

The Ministry of Finance updates the FA schema on scheduled effective dates. If your submission crosses the switchover, the same XML that validated yesterday against FA(2) can fail today against FA(3). Check the currently active schema URI on the /online/Session endpoint.

Where do I get the official FA XSD?

The Ministry of Finance publishes FA schemas at gov.pl/web/kas under Struktury dokumentów XML. Always validate locally against the exact XSD before sending — do not use KSeF as your development validator, or you will consume your rate-limit quota on schema errors.

Which ERPs produce the most 21401 errors?

During any FA schema transition (FA(2) → FA(3), and future 2026 hotfixes), any ERP with a manual mapping layer — SAP DRC, Comarch, custom Odoo — sees a spike. Vendors with centrally-maintained connectors (Symfonia SaaS, Fakturownia) get the schema update automatically.

Error codes · ksef · Poland

KSEF-21401In your invoicing software

Document does not conform to the KSeF XSD schema

This is the rejection, word for word: „[KSEF-21401] KSeF error 21401 ("Dokument nie jest zgodny ze schemą (xsd)") is returned when the invoice payload fails XSD schema validation against the FA schema published by the Polish Ministry of Finance. The API rejects the payload before any business validation runs, so no reference number is issued and the invoice is not stored.“

The KSeF ingestion pipeline validates every submission against the currently active FA schema (FA(2) or FA(3) for KSeF 2.0). Validation happens synchronously on /online/Invoice/Send and asynchronously on batch endpoints. When it fails, the API returns HTTP 400 with exceptionCode 21401 and, when available, an exceptionDetailList of XPath locations and XSD messages.

What to have readyNothing. The file has to be re-exported from your invoicing software; we check it again afterwards.

What we doRegenerate the invoice against the exact FA schema version declared in the session header, fix each schema violation using the exceptionDetailList (missing required elements, wrong data types, wrong element order, unknown namespaces), and resubmit.

Choose the rejected invoiceor drop it here

XRechnung XML or ZUGFeRD PDF. Checking is free · corrected file €1.90 · the first every 30 days is free · no sign-up.

What the finding looks likeExample

FindingStructure invalid · KSEF-21401

From youA re-exported file

ThenRe-export

ProofSHA-256 and /verify link after the check

Often appears together with

KSEF-440KSeF Duplicate Invoice Rejection (HTTP 440)