How do I send event Properties?

I use the following code in my Flutter app / Dart:

   Amplitude.getInstance().setUserId(userID, startNewSession: false);

   Amplitude.getInstance().logEvent(actionName, 
                                    eventProperties: {
                                      'pageName': pageName
                                     }
                                   );

When I check the Event Stream, I see the pageName property as an Event Property.

But when I attempt to create a chart to GroupBy page Name for a given actionName...I don’t have that option.