KSeF implementation and accounting systems

We connect the company system to the National e-Invoice System. We build issue and receive of e-invoices and a flow that accounting actually opens. We do not replace a tax adviser and we do not keep the books. We deliver software: an API session, an FA(3) document, status, UPO and a record in the company process.

What applies — and what we do not promise

From 1 February 2026 receiving invoices in KSeF is mandatory. Issuing: from 1 February 2026 for taxpayers whose 2024 sales exceeded PLN 200 million gross; from 1 April 2026 for the rest — except the smallest, who may stay outside the issuing duty until the end of 2026. The FA(3) logical structure applies from 1 February 2026. Dates and exclusions are set by the Ministry of Finance — an offer does not guarantee a tax reading, only that the integration works.

KSeF 2.0 API integration

Authentication, permissions and tokens on the taxpayer side. An interactive or batch session — per MF documentation. XML invoice matching FA(3), encryption the API requires, a session reference, processing status, a collective UPO after close. A test environment before production. Failures and rejections return to the operator with a readable reason, not as a bare 500.

Issue and receive in the company process

Issue: the document is born in sales or the ledger, passes field checks, goes to KSeF, comes back with a number. Receive: periodic pull of purchase invoices, preview, assign to a case, an order or a register. Offline and fallback modes — only in the range MF allows and we can keep. A PDF view is a convenience; the source document remains the e-invoice in KSeF.

Building accounting systems

Where a flow is missing: sales and purchase register, a working posting, export to an existing ledger, corrections, rights for the bookkeeper and the signer. We can build an invoice module from scratch or wire KSeF into a system that already stands. We are not an accountancy firm. Accounting scope in an offer is system functions, not a bookkeeping service.

Security and who holds what

KSeF certificates, tokens and accounts stay with the company unless the offer says otherwise. We log who sent, who pulled, which status came back. Test and production stay apart. Invoice data — including NIP and amounts — does not go into a public AI model. A change of the FA schema or the MF API is a later stage when MF publishes a new version.

First stage

One path: either issuing one invoice type on the API test environment, or receiving purchase invoices and a list in the company system. UPO, status and two roles. After sign-off: corrections, attachments, posting, export to the ledger or the other direction (issue or receive) — a separate quote.