Unable to activate Plesk license: Make sure that connections to the license server ka.plesk.com on TCP port 443 are not blocked

Symptoms

Unable to activate Plesk license with the below error:

Could not update the license. Make sure that connections to the license server ka.plesk.com on TCP port 443 are not blocked. See how to do so.

Cause

Only external/private name server is specified in /etc/resolv.conf file.

Resolution

1. Connect to the server via SSH.

2. Add public name server to the /etc/resolv.conf file using text editor:

   nameserver 8.8.8.8