Guide

Correction to zero, manual line-item editing, correction from XML and correction from the KSeF invoice list. See how to prepare a corrective invoice in KSeFGPT.

Free PDF to XML KSeF converter - just an email address. Step by step: how to turn a PDF invoice into FA(3) and submit it to KSeF in 2026.

How long do you have to send an invoice to KSeF? Deadlines in online, offline24, unavailability and failure modes. Specific days and legal basis 2026.

How to mass-send invoices to KSeF: batch sessions, CSV structure, FA(3) mapping, validation, and bulk import with KSeFGPT.

How to submit invoices to KSeF in 2026: modes (online, offline24, unavailability, failure), authentication, UPO, limits, common errors and free tools.

Discover the most common KSeF implementation challenges in 2026: XML validation errors, invoice visibility problems, contractor data quality, and emergency situations. Learn how to solve them effectively.

Poland's mandatory e-invoicing system covers virtually all VAT taxpayers from April 2026. Find out who is exempt and what the penalties are.

No. KSeF does not accept a PDF as a valid invoice. You submit FA(3) XML to the system; a PDF serves only as a visual representation or a source for conversion.

Self-billing reverses the roles — the buyer issues the invoice on behalf of the seller. In the era of mandatory KSeF, this requires proper permissions and a tool for mass document submission. Find out how it works and how ksefgpt solves it.

Retyping one invoice seems trivial — the problem starts when there are a hundred per month. From February 2026 KSeF becomes mandatory. A guide to PDF-to-XML conversion, validation pitfalls, and choosing the right tools.

We explain the differences between tokens and certificates, show you how to generate them, and when to use each.