What is auto SSL in cpanel hosting?
AutoSSL is a free alternative to paid SSL certificates. Your SSL certificate stays up-to-date and auto-renews on your behalf.
You can read more about auto SSL on this website
In order to run auto SSL you would need to make sure IP address of domain is pointing to the server IP address otherwise you would get error.
Above article has complete info on steps you need to follow to make sure SSL certificate run smoothly