Troubleshooting Tip: Unable to unregister FortiGate from FortiManager - Error 'Please unregister-device from FortiManager first. -582'

[Umer221]

Description	This article describes how to fix an issue where, when trying to change the central management type from FortiManager to FortiGuard or none, administrators may run into an error that prevents them with the error 'Please unregister-device from FortiManager first. -582'.
Scope	FortiOS, FortiGate, FortiManager.
Solution	The error: A FortiManager serial number will be necessary to proceed further. Upon obtaining the serial number, run the following commands as shown in the photo: Finally, set the type to either 'FortiGuard' or 'none' using the following commands: