Self-written POS system, is it legal and what are the pitfalls?

Question

Programming

Hello!
I am preparing a system for accounting for the receipt of goods and services for the customer. Roughly speaking - a special system for accounting for the operation of a commercial facility.
There is a cashier's workplace, where it is indicated how much money and for what services to take. The customer asks to integrate this with a receipt printer, cash drawer and card payment terminal. If everything is clear with the payment terminal, there is an SDK on the ingenico website, then I don’t understand what to do with a receipt printer and a box.
Common sense tells me that in order for sales to be legal, you need a licensed cash register. And through it checks are printed.
Which device is suitable for me and is the equipment designed to be connected to it from the outside? I am ready to work with com ports, with raw tcp, with any technology. But I don't know where to start!
I know that in Russia they use ATOL.RU products, they have a site with downloads, apparently, you need to have a username and password to download something: atol download center
Thank you in advance.

Answer 1

> If everything is clear with the payment terminal, there is an SDK on the ingenico website
Do not forget that you are subject to PA DSS