I just purchased this plugin. I downloaded the latest version in Client Area, added the zip file to the Add New section of the WordPress plugin dashboard.
For a moment there was an extra section in WP dashboard that said “Enter API Key” or something like that. I entered it as shown in Client Area, but it just took me to a “You are not authorized to access this area” page.
When I got back to my dashboard the API section was gone and there is also not a settings area for this plugin anywhere in my dashboard.
The plugin appears installed and activated correctly.