KSEF-001:NIP validation failed
Fix: Verify the NIP is 10 digits with valid checksum. Provide the required value in the free validator.
Polish NIP (tax identification number) must be 10 digits with valid checksum. Both seller and buyer NIP are required for B2B invoices. Leading zeros are significant.
Engine Classification
Business data required · Explicit input workflow · No assumptions made
Required input: Polish NIP (Tax ID)
What is KSEF-001?
KSEF-001 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-001 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-001
- ·Specification: KSeF
How to Fix It
Technical Reference
Code Example
<NIP>1234567890</NIP>Common Causes
- ·NIP entered with only 9 digits
- ·Invalid checksum
- ·NIP cancelled or inactive
Seeing this in production? The API handles KSEF-001 automatically. See the fix response →
Frequently Asked Questions
Polish NIP (tax identification number) must be 10 digits with valid checksum. Both seller and buyer NIP are required for B2B invoices. Leading zeros are significant.
Verify the NIP is 10 digits with valid checksum. Invoice Navigator detects this error and prompts for the required business data before applying a safe fix.
Yes, KSEF-001 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-001 requires specific business data to resolve. Invoice Navigator detects the error and guides you through providing the needed information, then applies the fix with full audit documentation.
Related Content
Last updated: 3 March 2026
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