🇵🇱 KSEF-21177: Invoice issue date is outside the allowed KSeF window in Poland
KSEF-21177 is a server-side validation error returned by the Polish Krajowy System e-Faktur (KSeF) when the FA(2) schema element P_1 (data wystawienia / invoice issue date) is outside the window the platform accepts. KSeF rejects invoices whose issue date is in the future, more than the allowed look-back from the submission timestamp, or in a different reporting period than the one the schema header (DataWytworzeniaFa) declares. The mandate-live behaviour since the February 2026 go-live is strict: the platform returns 400 with this code and the invoice is not stored.
Why This Matters in Poland
Poland requires e-invoicing using KSeF XML format. Invoices with this error will be rejected. They cannot be processed for Poland compliance.
How to Fix KSEF-21177
Normalise P_1 to Europe/Warsaw before serialisation; for genuinely backdated invoices switch to the correction (KOR) flow; for future-dated invoices hold submission until the issue date arrives.
Example: Before & After
<P_1>2026-04-15</P_1> <DataWytworzeniaFa>2026-05-05T09:30:00Z</DataWytworzeniaFa>
<P_1>2026-05-05</P_1> <DataWytworzeniaFa>2026-05-05T09:30:00+02:00</DataWytworzeniaFa>
Poland E-Invoicing Requirements
Fix KSEF-21177 automatically
Upload your invoice and let Invoice Navigator auto-remediate this error.