KSEF-003:Invoice number sequence gap
Invoice numbers must be sequential without gaps within each calendar year. KSeF rejects invoices with numbering gaps or duplicates.
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). It checks whether invoice number sequence gap.
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-003 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-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. You can also use Invoice Navigator's automatic Fixer tool to correct this instantly.
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.
Many instances of KSEF-003 can be automatically corrected using Invoice Navigator's Fixer tool. Upload your invoice and the tool will identify and fix common issues, including invoice number sequence gap.
Last updated: 19 January 2026
Handle KSEF-003 Automatically in Your Pipeline
The compliance engine auto-remediates this error with controlled safety policies and evidence pack generation.