KSeF date format invalid — wrong date or timestamp serialisation in Poland

This is the rejection, word for word: „[KSEF-007] KSEF-007 is raised when a date or timestamp in an FA(2)/FA(3) e-invoice does not match the format the KSeF (Krajowy System e-Faktur) XSD requires. The Polish schema uses two different date types: plain calendar dates such as P_1 (data wystawienia / issue date), P_6 (sale date) and the due date must be xs:date in YYYY-MM-DD form, while DataWytworzeniaFa (the technical document creation timestamp in the header) must be a full xs:dateTime with a UTC time-zone designator. Any other shape — a localised 15.04.2026, a slash date, a two-digit year, a date-only value placed in DataWytworzeniaFa, or a timestamp missing its Z / +02:00 offset — is rejected before the business checks even run.“

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.

Polish B2B e-invoicing runs through KSeF under the national mandate. A document KSeF will not accept is not legally issued for VAT — a schema-level date error blocks the invoice at the gateway.

What to have readyThe missing value from your purchase order, contract or bookkeeping.

What we doNormalise every calendar-date field (P_1, P_6, P_6A, due dates) to YYYY-MM-DD and serialise DataWytworzeniaFa as a full timestamp with an explicit UTC designator, e.g. 2026-06-16T09:30:00Z or 2026-06-16T11:30:00+02:00. Do the formatting at serialisation time with an invariant/ISO formatter rather than the system locale. Keep the calendar value (P_1) independent of the timestamp's time zone — P_1 is evaluated by KSeF in Europe/Warsaw, so derive it from the Warsaw-local date. Invoice Navigator normalises these deterministically, which is why the fix confidence is high.

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How to fix KSEF-007

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If you enter it yourself in your invoicing software

Before

<P_1>15.04.2026</P_1>
<DataWytworzeniaFa>2026-04-15</DataWytworzeniaFa>

After

<P_1>2026-04-15</P_1>
<DataWytworzeniaFa>2026-04-15T09:30:00Z</DataWytworzeniaFa>

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

The schema is strict about ISO 8601 and most failures come from the ERP serialising dates the way a Polish or German locale displays them.

Read on

KSEF-007, the full explanation →Poland e-invoicing guide →All Poland error codes →