Firstly install Let's Encrypt or SSL It extension on Plesk, next create a service plan, under the service plan you created go to "Additional Service", depending on which of the above extension you install, select "Keep websites secured with free SSL Certificate"
SSL will be installed on the plan.
I've tested it before on Ubuntu and it works, decided to change to Centos and seems like I have to manually install the SSL each time a physical hosting is provisioned.
Under Service plan->Additional Services->Let's Encrypt->Keep websites secured with free SSL Certificate is enabled, but I have...