When try to add new device: "A device with serial number FGTXXXXXXXXXXXXXX already exists"

Hi Team,

When try to add new device to fortimanager, we are getting "A device with serial number FGTXXXXXXXXXXXXXX already exists".

When cross checked the fortimanager, this is a new firewall to fortimanager where this firewall never added to fortimanager before.

Regards,

Sridhar S