The secret key is used to link one of our official plugins with your server so your players can receive the packages they have purchased.
If you haven't already created a server you can do so by heading over to the servers page of your control panel. When creating your server ensure that you select the "Game Server" type as this is the only server type which provides you with a secret key.
After you have created your server, click edit, and then you will see your secret key. For security purposes we don't display your full secret key, however you can view it by clicking "Show Secret Key".