Troubleshooting Tip: How to fix error '(errcode)-999 - channel X is not supported' in FortiManager 7.4

[haldahan]

Description	This article describes how to fix the ‘(errcode)-999 - channel X is not supported’ in FortiManager 7.4.
Scope	FortiManager.
Solution	The error: This issue appears after upgrading FortiGate to 7.4 release where: FortiManager is managing 7.0 or 7.2 ADOMs. FortiGates are managing FortiAPs. Apply the following workarounds to fix the error: '(errcode)-999 - channel X is not supported': Disable central management and create new AP profiles/templates to be assigned to the 7.4 FortiGates and its FortiAPs. Use a CLI/Jinja template to override the band configuration. The ADOM version and FortiGate version must be the same to solve this error permanently.