Two Months with Mandatory KSeF — Stabilizing
Two months into mandatory use of the National e-Invoicing System (KSeF), the situation is stabilizing. Most early performance and validation issues have been resolved, and the Ministry of Finance has rolled out several important improvements. At the same time, new challenges have emerged that could not have been predicted in the first week.
What the Ministry of Finance Improved
- Higher API rate limits — raised from 60 to 120 calls per minute for accounting integrations, improving stability of bulk invoice issuance
- Clearer error messages — particularly for buyer NIP and GTU code validation; errors are now descriptive rather than just numeric
- Documentation updates — new FAQ sections on corrections, advance invoices, and edge cases (e.g., self-billing)
- Emergency mode — clarified rules for use during taxpayer-side outages (not just KSeF outages)
Most Common Practical Issues
From what we see at our clients, the biggest difficulties in the first two months are:
- Invoices issued outside KSeF by foreign counterparties — questions arise about how to book a PDF sent by email when the issuer is not a Polish VAT taxpayer
- Corrections to invoices issued before March 1, 2026 — should they be issued in KSeF or outside? MF clarified: corrections to paper invoices are issued in KSeF if the issuer is now covered by the obligation
- Advance and final invoices — proper linking of advance invoices to the final invoice via the "advance invoice" field
- Issue date vs. receipt date — in KSeF, the receipt date is the moment a KSeF number is assigned, sometimes a few seconds after submission; in practice this does not affect VAT settlement
KSeF Number as a Trade Reference
A noticeable trend is the use of the KSeF number as a reference in bank transfers. More and more companies require it in payment descriptions, which speeds up reconciliation. Some banks now offer KSeF invoice import directly from the business banking interface.
KSeF Numbers — First Two Months
| Metric | Value (approx.) |
|---|---|
| Invoices issued | over 600 million |
| Average KSeF number assignment time | under 1 second |
| System outages (> 30 min) | 2 incidents |
| Active issuers | ~1.8 million taxpayers |
What to Watch in May and June
- First VAT returns with KSeF invoices for March and April — make sure JPK_V7 reconciles with KSeF numbers
- Process audit — are purchase invoices pulled from KSeF systematically, or do you check daily?
- KSeF permissions — review who has rights to issue and receive on the company's behalf
- Foreign-currency invoices — remember to use the correct NBP rate from the day before
We help clients adapt their accounting processes to KSeF, audit permissions, and assist with corrections. Contact us to optimize your company's invoice flow.