I went over to z-lib.is and found that first, my old account was no longer recognized; and second, it wouldn’t let me access any books. It just redirected me to some page asking me to purchase a “lifetime premium membership.” What’s going on there?

ETA: Z-Library’s domain was taken down some time last year. They’re now available through TOR, and the onion link is on Wikipedia: https://en.wikipedia.org/wiki/Z-Library

Don’t give your money to whoever is running the .is site!