Submit batch invoices to Poland KSeF 2.0 using FA(3) schema

Steps

1. Obtain a KSeF authentication token by calling the session initiation endpoint with your NIP and a signed challenge; the KSeF 2.0 API uses OpenAPI 3.0.4 and all session calls require a valid token in the SessionToken header.
2. Build each invoice as a valid FA_VAT(3) XML document; FA(3) is the only accepted schema from 1 February 2026 — FA(2) documents will be rejected.
3. Wrap multiple FA(3) invoices in a batch envelope according to the KSeF 2.0 integration guide and POST the batch payload to the batch invoice submission endpoint documented in the interactive KSeF 2.0 API portal.
4. Poll the batch status endpoint with the returned reference number until the status changes to PROCESSED or REJECTED.
5. For each accepted invoice, retrieve the UPO (Urzedowe Poswiadczenie Odbioru) from the UPO endpoint using the invoice's KSeF number — the UPO is the legally binding receipt of acceptance.
6. Store the KSeF number and UPO for each invoice; these are required for audit and buyer reference.