errorPOLKSeF

KSEF-007:Date format invalid

All dates in KSeF invoices must be in YYYY-MM-DD (ISO 8601) format. Other formats are rejected.

Fix this in your source system

MANUAL

Dates must be in YYYY-MM-DD (ISO 8601) format for KSeF. Automatic date format conversion is not safe due to ambiguity (e.g., 01/02/2024 could be January 2nd or February 1st). Configure your invoicing software to output dates in ISO 8601 format.

See the step-by-step instructions below to fix this error manually.

How to Fix It

Code Example

<DataWystawienia>2026-02-15</DataWystawienia>

Common Causes

  • Polish date format DD.MM.YYYY used
  • Incorrect separator
  • Software default format wrong

Frequently Asked Questions

All dates in KSeF invoices must be in YYYY-MM-DD (ISO 8601) format. Other formats are rejected.
Use ISO 8601 date format (YYYY-MM-DD). You can also use Invoice Navigator's automatic Fixer tool to correct this instantly.
Yes, KSEF-007 is a critical error that will cause invoice rejection. It must be fixed before submission to ensure your invoice is accepted by the recipient's system.
Many instances of KSEF-007 can be automatically corrected using Invoice Navigator's Fixer tool. Upload your invoice and the tool will identify and fix common issues, including date format invalid.

Last updated: 19 January 2026

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