After buying the plugin you received an confirmation email including your personal license key. This key is required in order to receive automatic updates including bug fixes, new functionality and more.
Additionally the license key authorizes you to use the plugin and determines how many WordPress installations are allowed to be used with (depending on which license you bought).
After every first plugin installation you must activate your license for this single website.
In case you want to use the plugin on another site (assuming that you don't own a developer license) you first have to deactivate the current site and after that activating the new site again.
You want to use the plugin on more than one website? That's amazing! Go to your account page and upgrade your existing license.
For any problems about licensing please don't hesitate to contact us.