Java.LangNoSuchMethodError when trying to use getBluetoothLeAdvertiser

I am using Android.Bluetooth, and using Android.Bluetooth.LE;

My API version is 7.1 in forms
The phone is running 4.4.2

My class is:
class BluetoothLEManager : Java.Lang.Object, BluetoothAdapter.ILeScanCallback

I am able to scan for devices using .StartLeScan
But when I try to get an advertiser object it says there is no such method as: getBluetoothLeAdvertiser

Any ideas? It comes up on intellisense, so not sure why this is the case.
Does the phone version need to be upgraded?

Best Regards,
Eric