If your server is behind NAT and doesn't have a public network interface, the panel has to be activated with a license key after it is installed. In order to do that you need to:
Open the panel billing account
Select a license that is directed to the public IP-address of your server
Copy an activation key
Paste the activation key into the corresponding form of the panel license activation window
How does the activation key works?
The activation key is created automatically when a license is ordered. You can get your activation key by double-clicking a key icon of a corresponding license.
The activation key can be used only once. In case the license is required to be activated again, a new key need to be generated as well. A new key can be generated once in a month in your billing account or it can be requested via Technical Support.
To activate a license with a key, the license server has to be available from the server where the panel is installed. To check the license server availability you may run the following command on the server where the panel is installed:
mogwai licence ping-server