KSeF Invoice Errors — Overview and Solutions
Two weeks into mandatory KSeF, clear patterns of recurring errors have emerged. Many stem from incorrect accounting software configuration or misunderstanding of how the system works.
1. Incorrect Buyer NIP
The most common error. An invoice with the wrong buyer NIP is considered validly issued, but the recipient won't see it in their KSeF account. Solution: Issue a correcting invoice zeroing out all items, then issue a new invoice with the correct NIP.
2. Incorrect GTU Codes
GTU codes are required for specific transaction categories. Common mistakes include using wrong codes or omitting them entirely. Issue a correcting invoice with the proper GTU code.
3. Sale Date Errors
The issue date is assigned automatically by KSeF. The sale date (delivery/service date) must be entered by the issuer. Invoices can be issued up to the 15th of the month following the sale.
4. No Duplicates in KSeF
KSeF has no concept of duplicate invoices. Each invoice has a unique KSeF number and is stored for 10 years. Share the KSeF number with the buyer so they can find it.
5. XML Validation Errors
Common issues: empty required fields, incorrect amounts (rounding errors), special characters needing XML encoding. Use the XML validator before sending.
6. Correction Rules
Correcting invoices must include the original KSeF number, reason for correction, and corrected data. No buyer confirmation needed (SLIM VAT 4 change).
How to Avoid Errors
- Keep software updated
- Verify buyer data against the VAT whitelist
- Test on the demo environment
- Always check invoice status after sending
Need help with KSeF invoices? Contact us.