GURU Cloud automatically provides a Let's Encrypt free SSL certificate for all hosted domains.
This includes all addon/parked domains and all domains hosted within reseller accounts.
You do not have to do anything to enable this feature, as the SSL certificate will automatically be generated within 24 hours of your domain resolving* to your GURU Cloud service.
* SSL certificates can only be created when your domain is active with GURU, because this enables Let's Encrypt to perform validation of your domain.