There's no terminal window inside WordPress. You need to access it on the server where WordPress is installed. Typically you ssh into your WordPress server and that's your terminal.
Listly mentions 4.5.4, but works with 4.6.1. We have to make a small update to mention 4.6.1.
Where is your WordPress server hosted? Is your WordPress server installed behind a corporate/educational organization's firewall? If so, you might check with your network admin and ask them to allow traffic back and forth to Listly servers. They might have to whitelist Listly servers.