Audience Ids returning null | SharePoint REST API

I ran into this yesterday and finally found a solution.  The issue is with the endpoint you are using.  That is, you'll need to use either: _api/navigation/menustate?mapprovidername='CurrentNavigationSwitchableProvider' OR _api/navigation/menustate?mapprovidername='GlobalNavigationSwitchableProvider' and then search for your item.  The Audience is a custom property which contains the Group Names (not the ids of the groups).