It's very simple to install the "Let’s Encrypt" SSL Certificate for the hostname. Here are the steps:
# hostname host.domain.com
# v-add-letsencrypt-host
If you don't like to use the above command, you can follow the steps mentioned on this page: https://www.bitsdiscover.com/how-to-use-lets-encrypt-ssl-certificate-for-hostname-on-vestacp-or-hestiacp-login-panel/