Hi HPC. I'm Greg, awarded MVP for eleven years, Volunteer Moderator, and Independent Advisor here to help you until this is resolved.
I would not buy anything from that site. They are almost certainly not legitimate. Even if they activated for awhile, that would just mean they are Volume License Keys which can only legally be used by organizations, they would expire when they couldn't connect to the company's server to reactivate periodically.
There is more explanation for this here:
https://www.howtogeek.com/392080/cheap-windows-...
I would buy retail keys only from major retailers who back all sales, or directly from Microsoft here:
https://www.microsoft.com/en-us/p/windows-10-ho...
You may still be to get free Windows 10:
https://www.groovypost.com/howto/download-windo...
https://www.zdnet.com/article/heres-how-you-can...
https://www.reddit.com/r/buildapc/comments/6fdg...
I hope it helps.