What could be happening here could be caused by a plugin conflict. Could you temporarily disable all the non-toolset plugins and try performing the registration again ?
There seems to be an error in the maker's code. Whenever one tries to activate the license key, it causes a "PHP Fatal error"
(see postscript). Perhaps their coders can make sense of this error.
We are using version 7.2 of PHP.
PHP error returned by license activation:
PHP Fatal error: Uncaught TypeError: Argument 2 passed to OTGS_Installer_Source::__construct() must be an instance of WP_Filesystem_Base, null given, called in /var/www/wordpress/widapl/wp-content/plugins/types/vendor/otgs/installer/includes/class-otgs-installer-source-factory.php on line 10 and defined in /var/www/wordpress/widapl/wp-content/plugins/types/vendor/otgs/installer/includes/class-otgs-installer-source.php:8#012Stack trace:#012#0 /var/www/wordpress/widapl/wp-content/plugins/types/vendor/otgs/installer/includes/class-otgs-installer-source-factory.php(10): OTGS_Installer_Source->__construct(Object(WP_Installer), NULL)#012#1 /var/www/wordpress/widapl/wp-content/plugins/types/vendor/otgs/installer/includes/site-key/class-otgs-installer-fetch-subscription.php(59): OTGS_Installer_Source_Factory->create()#012#2 /var/www/wordpress/widapl/wp-content/plugins/types/vendor/otgs/installer/includes/site-key/class-otgs-installer-site-key-ajax.php(40): OTGS_Installer_Fetch_Subscription->get('toolset', 'tLWzsEUCOJ', 3)#012#3 /var/www/wordpress/w in /var/www/wordpress/widapl/wp-content/plugins/types/vendor/otgs/installer/includes/class-otgs-installer-source.php on line 8