I've got a bunch of websites, secured with LetsEncrypt certificates through ISPConfig, and they've failed to auto-renew last night. I'm not sure why exactly, as it obviously worked in the first place, in order to obtain the certificates to begin with. What "challenges" does ISPConfig use with LetsEncrypt / Certbot? Because if I know what it's attempting to do, then I can investigate more closely why it's suddenly decided not to work. Or possibly some setting has gone wrong. I don't know. I need guidance as to how to diagnose and fix this.