After you enable Closed Network on NSM, you need to associate which firewalls are managed by NSM.
To associate the NSM with the Firewall
Log into MySonicWall.
Navigate to My Workspace > Products in MySonicWall.
Select the NSM for which you have enabled the closed network.
Click on Managed Nodes.
Select the serial number of the firewall to associate with the NSM.
Click Associate.