location permission

I'm building an app which needs acces to the device' GPS.
I followed this tutorial (https://github.com/jamesmontemagno/PermissionsPlugin) but the app doesn't prompt me to ask for permissions.
I've got this code in my mainactivity:
public override void OnRequestPermissionsResult(int requestCode, string[] permissions, Permission[] grantResults) { PermissionsImplementation.Current.OnRequestPermissionsResult(requestCode, permissions, grantResults); }
This are the permissions in my AndroidManifest:
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" /> <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" /> <uses-permission android:name="android.permission.INTERNET" />