This is a problem usually encountered by customers who are configuring their ZXTM software/appliance offline, then transporting it, fully configured, to their datacentre to be made live.
ZXTM verifies IP-bound licence keys by confirming that the IP address in the licence key is raised on a network interface that is physically connected to a switch/router and has an active link (i.e. ifconfig reports its state as RUNNING).
Before contacting Zeus Support please make sure that the IP and interface that Zeus' license.key is expecting to be raised is in the RUNNING state. This is usually achieved, very simply, by physically plugging in an ethernet cable connected to your network.
If, after performing the above, ZXTM is still reporting your license key as invalid please contact Zeus Support including the serial number of your license key.