How to break site inheritance and add user to permissions group in sharepoint using REST api

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REST

SharePoint2013

Hi,

I am trying to add a user to a site permissions group.
As i understand, i need to break inheritance first, get all the permission groups and add the user to the required permission group.

The problem is, that i can't find any documentation nor examples of how to do it.
I found lots of examples for lists but not for site

is there a way?

Thank you

What I have tried:

all things i tried were related to lists, thus it did not help