The following warning is displayed in Plesk at Domains > example.com > Let’s Encrypt:
PLESK_WARN: Warning: SSL/TLS support is disabled for example.com.
To resolve the issue, please enable to SSL/TLS support (“Websites & Domains” > “Hosting Settings”) for this domain and try again.
The “Get it free” button is grayed out or it is only possible to secure webmail for a domain (other options are missing) at Domains > example.com > SSL/TLS Certificates > Let’s Encrypt:
It is not possible to install SSL certificate when SSL/TLS support is disabled. The behavior when there is no warning about disabled SSL support is considered as a bug wit ID #EXTLETSENC-871.
Go to Domains > example.com > Hosting Settings.
Enable SSL/TLS support.
Apply the changes.