Object category &2 is not intended for notification type &1

What causes this issue?

The object category is not stored in Customizing for the notification
type.

System Response

Objects with this category cannot be assigned to the notification item.
The system terminates the action.

How to fix this error?

Assign objects that have one of the planned categories or contact your
system administrator. You system administrator can adjust the
notification type accordingly.

Procedure for System Administrators

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Error message extract from SAP system. Copyright SAP SE.