Why firewall shows "Unmanaged" and "Out of Sync" in NSM!

Firewall is online but shows Unmanaged and Out Of Sync in NSM.

Though firewall is online but shows "Unmanaged" in NSM under Manager View-->Firewall--> Inventory.

When a device is acquired in NSM, it is recommended to make firewall configuration changes via NSM.

When there a config change is done on the firewall locally, the firewall goes "Out Of Sync" in NSM. In order to Sync it back in NSM, firewall needs to synchronized manually in NSM.

Steps on how to sync a firewall in NSM: How to sync a firewall in NSM.