For those who can’t register to playonlinux, I found the problem. It’s how you enter the register fields. You need to paste your email address then --press enter-- on that line. If you don’t press enter, the “check mail…” link won’t work.
email address field->paste email address grey text: “check email…” button
Cursor in email address field. Press enter. black text: “check email…” button
(not sure if correct forum, move if needed). testing it…