How does IP address restriction work?

So I have used some services which are supposed to work only one time on a computer/IP and I have always wondered how those work. I even took my laptop to a different home which has a different IP on a different wireless router and still it works great that it recognized that i have already used it.

How does the technology behind this work? Do they use MAC addressses as well? I'm just fascinated by how well done it is and how it actually works!

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