Guides
KSeF Kit guides
KSeF 2.0 guides: the mandate, structured invoices, corrections and the Stripe integration.
Basics
- KSeF Mandatory 2026: Deadlines, Thresholds, Who KSeF is mandatory from 1 February 2026 for firms with sales above 200M PLN and from 1 April 2026 for all other VAT payers. The smallest: 1 January 2027.
- UPO in KSeF: What the Confirmation Proves UPO proves KSeF accepted your invoice and assigned it a number. Without a UPO the invoice was not issued, so archive every confirmation with the invoice.
- KSeF for sole traders: do you actually have to? A Polish sole trader (JDG) must issue invoices in KSeF from 1 April 2026, but only for sales to businesses. Consumer sales stay outside the mandate.
- Aplikacja Podatnika KSeF: the Ministry of Finance's Free App Aplikacja Podatnika KSeF is the Ministry of Finance's free web app at ap.ksef.mf.gov.pl. Issue and receive invoices, download UPO. Who is it enough for?
- GTU Codes on a KSeF Invoice: The GTU_01–GTU_13 List The full GTU_01–GTU_13 list with statutory scope, a table mapping common services to a code, and where the markers live in FA(3). Most invoices need none.
- KSeF Invoice Visualisation: the PDF Is Not the Invoice The invoice is the XML in KSeF; the visualisation is a picture of it. What a printout must carry, how to read an XML, and what to actually archive.
How it works
- How to Issue a Structured Invoice in KSeF Your tool builds an FA(3) XML from the sale data, you authorize a session and send it to KSeF, and KSeF returns a number and a UPO. Issue date = send date.
- KSeF QR Codes: KOD I, KOD II and Offline Mode An online invoice carries one QR code (KOD I), an offline or offline24 one has two: KOD I and KOD II. You compute them locally; the API never returns them.
- KSeF Correction Invoice (KOR): Fix a Filing An invoice with a KSeF number can't be cancelled. You issue a KOR correction in FA(3) referencing the original KSeF number; it gets its own number and UPO.
- KSeF Is Down: What to Do and by When to Send the Invoice KSeF down? You keep invoicing, outside the system. You then send to KSeF by the next business day — or within 7 business days after a declared outage.
Selling abroad
- Export Invoices and B2B Sales Abroad in KSeF Yes, B2B exports by a Polish VAT payer go to KSeF: goods, WDT and services, even at 0%. Outside KSeF: B2C, OSS/IOSS and firms not established in Poland.
- NBP Exchange Rates on Invoices in KSeF You report VAT in złoty at the average NBP rate from the last business day before the tax obligation arises (art. 31a(1)). Net and gross can stay in EUR.
Stripe + KSeF
- Stripe to KSeF Integration: FA(3) Step by Step A finalized Stripe invoice becomes an FA(3), goes to KSeF, and the KSeF number comes back. What you have to build, where it hurts, and what buying costs.
- Customer Data in Stripe for KSeF Invoices Two Stripe fields drive the VAT treatment: the customer country and the buyer tax id. Collect the name, address and NIP or EU VAT, or the sale stays B2C.
- Free KSeF for Stripe: File at No Cost Yes, you can file invoices to KSeF for free. KSeF Kit has a free production tier for Stripe users: no card, up to a monthly limit on a rolling month.
Deployment
- KSeF on Your Own Server: Deployment and Cost We deploy KSeF Kit on your servers for 2500 zł net one-time, no recurring fees. Updates cost 250 zł net each. Invoices and your KSeF token stay with you.
- KSeF API and SDK: What Integrating KSeF 2.0 Actually Takes What you really have to build to file an invoice through the KSeF 2.0 API: environments, authentication, sessions, encryption and the UPO. With Ruby examples and open source.
- The KSeF Test Environment: TEST, DEMO and Production The KSeF 2.0 test environment is ap-test.ksef.mf.gov.pl. The old ksef-test.mf.gov.pl address is dead. How TEST, DEMO and production actually differ.
- KSeF Token or KSeF Certificate: Which to Use A token is one paste; a KSeF certificate is free and valid up to 2 years. What 31 December 2026 changes, and why a token can't request a certificate.
- KSeF Integration: Five Routes and How to Pick Yours There is no single KSeF integration. There are five situations and five different answers. Work out which one you're in before you connect anything.