Setting notification.SoundName to default sound does not play the sound

Following this guideline,

http://docs.xamarin.com/guides/cross-platform/application_fundamentals/notifications/ios/local_notifications_in_ios/

I have added

notification.SoundName = UILocalNotification.DefaultSoundName

However when the local notification is received in the AppDelegate, no sound plays.

Checking notification.SoundName property in Immediate Windows displays "Not such method"

How do I get the default sound to play with my local notifications? I can explicitly load an audio file and play but I want to play the system notification sound

Thanks