After you've created the UM IP gateway, you must configure the physical device (referred to in the FQDN) to forward calls ...

After you've created the UM IP gateway, you must configure the physical device (referred to in the FQDN) to forward calls to the address specified in the Forwarding Address field. The forwarding address can be obtained from the Details page of the gateway or by running the Get-UMIPGateway cmdlet.