Our license agreement says: "One plugin can be installed on one single domain and its subdomains".
You can use the Pro license of our plugin for one website only. If you use our plugin on a different Wordpress websites, it is considered to be illegal use. If you would like to install the plugin on another website, you should remove plugin from the old website and only then install the plugin to a new one.
Learn how to fix that: http://support.bestwebsoft.com/hc/en-us/articles/204240089