System.NotImplementedException has been thrown in Xamarin Android

[huihuidou]

I got the following error when I am trying to call "CrossGeofence.Current.StartMonitoring()", it works fine on my iOS project.
I installed 1.8.11 version from NuGet package manager.

This functionality is not implemented in the portable version of this assembly. You should reference the NuGet package from your main application project in order to reference the platform-specific implementation.