Property decorators on properties#

A decorator like [Header] must be applied to fields that Unity serializes and displays in the inspector.

Resolution#

Don't decorate variables that aren't serialized, a property for example; instead decorate a serializable field.
That is a field that is marked with [SerializeField], or is public.

-[Header("Example")]
-public Example Value { get; private set; }

+[Header("Example")]
+[SerializeField] private Example _value;

If your field isn't visible, follow the debugging steps here.