Support for Untangle Router NG Firewall features is provided by the Untangle Support team and not the FlashRouter support team.
We recommend reviewing these excellent resources that Untangle has created to get you setup as desired.
To contact Untangle directly you can email them at support@untangle.com and their team would be happy to assist you with getting setup to use their NG Firewall settings such as Web Monitor, Captive Portal, Intrusion Prevention, and many other features supported by the Untangle firmware running on your FlashRouter.