What is the API key being used for?

I've read the official answer that it is used to so you can install the software. Specifically, I'd like to know what you do with the API key you generate? What sort of access will you have to my web server, etc? I ask because this appears to be a fully hosted (by me) solution so I'm curious why I would need to communicate with your API?

Thanks and I look forward to your reply.

It is used to install apps within one-click, nothing else:

https://akaunting.com/docs/user-manual/apps

I'd also add a detailed article about api - https://www.cleveroad.com/blog/what-is-an-api

In my case app ask for API key after instalation.