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KSeF and integrations with your store and Subiekt

KSeF, the National e-Invoicing System, is the Polish Ministry of Finance’s central system for issuing and receiving structured invoices. Integrations that issue or download invoices have to account for it.

Updated: 7 October 2026

What is KSeF?

KSeF (Krajowy System e-Faktur, Poland’s National e-Invoicing System) handles invoices as structured data instead of PDF files. An invoice sent to KSeF gets a number assigned by the system, and the buyer downloads it in the same form. The law decides which invoices the obligation covers and from when. Your accounting office or tax adviser can tell you how it applies to you.

How does KSeF affect store integrations with Subiekt?

If invoices are created automatically from store orders, the integration has to work with the submission to KSeF that the sales program carries out.

  • the store has to collect the buyer’s full details, including the NIP (Polish tax ID)
  • you decide when the invoice is issued: after the order, after payment or after shipping
  • the integration should handle a rejected invoice and a delayed submission
  • the KSeF number and the invoice status can be passed back to the order in the store

How does KSeF help with document workflows?

Cost invoices can be downloaded from KSeF automatically as data, without scanning or retyping. A document workflow system registers the invoice, routes it for description and approval, and passes it on to the accounting program.

Subiekt GT reports a connection error to the KSeF server: what should you check?

  • whether the program is on the current version
  • whether the KSeF credentials are valid and have the permissions needed
  • whether the company’s NIP and the selected KSeF environment are correct
  • whether a firewall or antivirus program is blocking the connection
  • whether the Ministry of Finance has announced an outage of the system

Frequently asked questions

Does KCD Studio integrate systems with KSeF?

Yes. We take KSeF into account in integrations between online stores and sales programs, and we build document workflow systems that download invoices from KSeF. See details

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