What is the best way to implement paid expansion work?

Question

User identification

There is some extension. It is planned that for its operation, the user must pay monthly, say, 100 rubles, or at once pay 500 rubles for permanent work.
Question: what is the best way to implement such a payment system? And how can you track that the person who paid for it is working with the extension (that is, more than one person paid for it and then resold it to others)? I understand that this is not a question that can be simply answered with code. I would like to understand in which direction we need to move and the algorithm, the easiest way to do this.
It is not expected that many people will use this extension, so I don’t think it makes sense to connect some kind of payment system. It will be possible to sell this extension to each person "manually". So I thought, to make a file with keys on the server, to issue a key to each new user who bought it. The user will enter it in the extension, the extension sends a request to the server, if the key is there, then the extension works. But there is a possibility that several people will use one key. So what is the best way to organize this whole system?

Answer 1

Raise a server with authorization and with data binding to the server of some important ones.
And it’s even better that they at least interfere with each other if several people use it at once.
But in general, on the server, make a limit on one possible session for one user, if he crashes - the extension does not work, it comes in - then all the others fly out.
This is done simply with a couple of ajax requests from the extension, it is also simple, but it is enough to protect against very mere mortals.

Answer 2

The Chrome Store has a paid distribution model