Another reason may be that you are using series that do not render separate items (Line, Spline, Area, Range, and all their stacked versions). For this type of series, the InteractivityScope.Item is not supported. In order to be able to select a PointMark on the line you need to use ChartArea_ItemClick event.
In case that these directions don't help you to solve the issue, could you please provide more information and code snippets about the implementation of RadChart.
Greetings,
Polina
the Telerik team
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