Poland is the fourth country in the European Union to introduce e-Invoice – API specification

The Polish Ministry of Finance on 20 October 2021 issued a specification for the National e-Invoicing System (NeIS), providing tips for software developers wishing to integrate their programs with NeIS (API). This specification is not a source of law, but is only a set of guidelines for developers. The NeIS test environment website ( does not contain a graphical user interface for uploading or downloading invoices. It contains material intended for IT departments working on integration with NeIS. This address is also used by the published API. The logical structures used by the API, the OpenApi (formerly Swagger) documentation and editor, and the test environment public key have been made available. For the time being, no descriptive interface specification has been published, as was the case for e-Declaration or the Single Control File. It has been indicated that the test version will use self-generated signatures and seals for authorisation in NeIS, the test version does not offer authorisation via the Trusted Profile and token at this point. Invoices will be submitted using the API provided in batch or interactive mode. An Official Delivery Certificate will be available with a list of invoices sent in a batch packet or during an interactive session. The provided service will verify the correctness of the sent invoices with the working version of the XSD schema. The API introduces permissions that can be assigned to a system user. A privilege management facility is provided that will allow to view, grant and revoke privileges. The types of roles available in the process are also indicated. It is worth noting that the message states that it is planned to make the use of e-Invoice mandatory for entrepreneurs in Poland from 2023.