It’s important to use the correct domain of the website, because most versions are scams.
You can see the scam versions and the official ones here. This is the dedicated subreddit to z library. For more general guides about the website you can check here.
If you use a VPN and it says that downloads for the IP address are finished, close the browser, search it again and just change the country until it works.
Otherwise, for the book Extreme privacy, you can go to Anna’s Archive and you won’t encounter this problem.
I got it from fhmy .net and from r/piracy, so it should be legitimate.