Unable to validate license

If you are unable to validate the license even after entering the license key correctly, try manually adding a site URL to the Manage Sites page (within the client area of Gravity Flow, Account -> License Keys ). You may need to remove a site that you had previously activated. 
If that doesn't work then it could be a firewall issue - this can be the case if your site is inside an intranet. You may need to modify the firewall rules to allow access to  https://gravityflow.io/.