If you license key is not being activated, please try remove any security plugins or deactivate them for the meantime. There have been a few cases of sites not being able to talk to our servers. If this doesn’t work, please do the following to create an error log for us to investigate further.
1) Set WP_DEBUG to true (https://docs.whmpress.com/faq/how-to-enable-or-disable-wp_debug-using-file-manager/
2) Try activating the license key
3) You can now set WP_DEBUG back to false
4) Submit a support ticket on our site with the URL of your site so we can check the log file.