To get your free SSL through Let’s Encrypt, you first need to have the domain added to your cPanel account, and have the DNS updated so that the domain points to the server. (This is important as Let’s Encrypt does validation of the site based on where it is hosted.)
Once you have the site added to your cPanel, and the DNS updated to point the site to the server, the AutoSSL Service will generate a new SSL for the domain. This process may take up to 24 hours as the AutoSSL Service is called once every 24 hours.
If you would like the SSL quicker, please verify that the DNS is updated to your server (https://www.whatsmydns.net/ works well to check this) and open a ticket to support. We can manually trigger the process for you and get your SSL typically much quicker, but it does depend on the DNS being up-to-date and the domain added to your account.