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On 30 September, the Ministry of Finance made API KSeF 2.0 available for testing. Entrepreneurs can now check whether their financial and accounting systems work with the National e-Invoicing System version that becomes mandatory next year.
What is KSeF and when does it become mandatory?
The National e-Invoicing System, KSeF, is the Ministry of Finance’s nationwide system for issuing, sharing and receiving structured invoices.
Described as an invoicing revolution, it will soon become mandatory for all domestic businesses.
From 1 February 2026, it covers entities whose 2024 sales exceeded PLN 200 million gross. The remaining companies must issue through KSeF from 1 April 2026.
From April to December, microbusinesses have a transition allowing exemption where monthly sales revenue does not exceed PLN 10,000 gross.
API KSeF 2.0 testing began on 30 September
As deadlines approach, many businesses are concerned about compatibility between their accounting systems and KSeF 2.0. The launch of testing on 30 September is therefore important.
The API exchanges information between KSeF and invoicing software. Testing checks whether the company’s system works with the version that becomes obligatory next year.
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Documentation and technical support
Businesses testing API KSeF 2.0 can use Ministry of Finance support. At the test environment, documentation includes:
- An integrator’s guide with ready-made API scenarios.
- An overview of key API changes.
- The OpenAPI 3.0.4 specification in JSON.
- Parameters, endpoints, data schemas, response codes and example calls.
- A .NET library with integration examples.
- A Java library with integration examples.
- The FA(3) logical structure.
The KSeF 2.0 handbook contains over 300 pages in four parts, from basics and everyday functions to additional options and matters for local-government units and VAT groups.
The technical team is available Monday to Friday, 7:00–19:00, through the contact form.
“Wednesdays with KSeF” training
The National Revenue Administration also launched free weekly training. Meetings take place every Wednesday from 24 September to mid-December, with online sessions and in-person workshops.
Details are available at Wednesdays with KSeF and on regional revenue-chamber websites.
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Summary
Testing gives businesses a chance to check software compatibility before mandatory invoicing begins. The documentation, handbook and training provide complementary support. For help organising your accounting, contact TaxCoach.
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