Here are the possible error messages, which return if any condition gets failed or required data is missing for processing.
The request could not be understood by the server due to malformed syntax.
You are not authorized to view the resource
Accessing the resource you were trying to reach is forbidden
The resource you were trying to reach is not found
No Event could be found
it is for the only host that can add a category and it is not then it will show this error Not Event Host
This setting is not allowed for your event plan