Engine Classification
Financial or legal field · Modification blocked by policy
Reason: KSeF requires sequential invoice numbers without gaps within each calendar year. This is a numbering policy enforced by your source system. Review your invoice numbering sequence and address any gaps before submitting to KSeF.
What is KSEF-003?
KSEF-003 is a fatal validation rule defined in the KSeF specification (POL national rules).
When this rule fires, the invoice is rejected by Peppol access points and never reaches the buyer.
Why This Error Matters
KSEF-003 is a hard failure — the invoice must be corrected and re-sent before it can reach the recipient.
Validator Behavior
- ·Causes invoice rejection
- ·Error returned: KSEF-003
- ·Specification: KSeF
How to Fix It
Technical Reference
Code Example
<NumerFaktury>FV/2026/00001</NumerFaktury>Common Causes
- ·Multiple systems using same number series
- ·Cancelled invoices leaving gaps
- ·Database restore issues
Seeing this in production? The API handles KSEF-003 automatically. See the fix response →
Frequently Asked Questions
Invoice numbers must be sequential without gaps within each calendar year. KSeF rejects invoices with numbering gaps or duplicates.
Ensure continuous sequential numbering per year. This error involves a protected field — Invoice Navigator flags it in your pipeline so your team can correct it at the source.
Yes, KSEF-003 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-003 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
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This error involves a financial field that can't be auto-modified. We'll flag it with a clear diagnosis so you can fix it at the source.