A few folks I know made a server a couple of days ago, I joined and started with them, when building my house I got stuck in the door due to lag and got kicked from the server. I logged back in and it seemed everything was fine. I logged in early today only to be told “Failed to Connect, Approval Denied”. I don’t know what the heck happened
Try playing on a different server and see what happens.
Maybe they’ve changed their server to have a whitelist mod, and you aren’t on it right now.