Your SimpleWAN device supports failover to a secondary connection in the event your primary connection has an issue. You can easily add this feature by contacting your Reseller/support agent and asking them to activate the feature as it needs to be added at an administrative level.
Once the Failover feature is activated, update the new WAN2 interface with the failover connection IP info (static, DHCP, etc.). Once that new information is saved, power down the SimpleWAN, plug the secondary connection into the OPT port and then power the SimpleWAN back up so that it can run a speed test on the failover connection for QoS settings. Be sure to go into the Diagnostic Tools section, and then click speed tests to verify that both a WAN and a WAN2 speed test were run. If there is no WAN2 speed test result, verify that the WAN2 information was input correctly, and reboot the unit again.