KSEF-007:Date format invalid
All dates in KSeF invoices must be in YYYY-MM-DD (ISO 8601) format. Other formats are rejected.
Engine Classification
Financial or legal field · Modification blocked by policy
Reason: 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.
What is KSEF-007?
KSEF-007 is a fatal validation rule defined in the KSeF specification (POL national rules). It checks whether date format invalid.
When this rule fires, the invoice is non-compliant and will be rejected by Peppol access points and national validation services. The sending system receives a rejection response and the invoice does not reach the buyer.
Why This Error Matters
KSEF-007 is a hard failure. Invoices that trigger this rule are rejected at the access point and never reach the recipient. In Peppol networks, this means your sending system receives an MLR (Message Level Response) with a rejection status. The invoice must be corrected and re-sent, adding delay to your payment cycle.
Validator Behavior
- ·Causes invoice rejection
- ·Error returned: KSEF-007
- ·Specification: KSeF
How to Fix It
Technical Reference
Code Example
<DataWystawienia>2026-02-15</DataWystawienia>Common Causes
- ·Polish date format DD.MM.YYYY used
- ·Incorrect separator
- ·Software default format wrong
Seeing this in production? The API handles KSEF-007 automatically. See the fix response →
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). This error involves a protected field — Invoice Navigator flags it in your pipeline so your team can correct it at the source.
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.
KSEF-007 involves a financial or legal field that cannot be auto-modified by policy. Invoice Navigator detects and flags this error immediately, but the correction must be made manually in your ERP or invoicing software.
Related Content
Last updated: 3 March 2026
Detect KSEF-007 Before Submission
This error involves a financial or legal field that cannot be auto-modified. The compliance engine flags it immediately with a clear diagnosis so your team can fix it at the source.