MatriX vNext doesn't connect in Android

Question

I am trying to create a simple XMPP client in Xamarin using the Matrix.vNext package.

I have this basic code on my MainActivity:

using Android.App;
using Android.OS;
using Android.Widget;
using Matrix;
using System.Threading.Tasks;

namespace XmppAndroid
{
    [Activity(Label = "@string/app_name", Theme = "@style/AppTheme", MainLauncher = true)]
    public class MainActivity : Activity
    {
        private ToastHandler handler;

        protected override void OnCreate(Bundle savedInstanceState)
        {
            base.OnCreate(savedInstanceState);
            SetContentView(Resource.Layout.activity_main);

            var button = FindViewById<Button>(Resource.Id.button);
            button.Click += delegate
            {
                Task task = new Task(Connect);
                task.Start();
            };

            handler = new ToastHandler(this);
        }

        async void Connect()
        {
            var msg = new Android.OS.Message();

            msg.Data.PutString("message", "Connecting...");
            handler.SendMessage(msg);

            var client = new XmppClient
            {
                Username = "username",
                Password = "123456",
                XmppDomain = "domain.com"
            };

            await client.ConnectAsync();

            msg.Data.PutString("message", "Connected!");
            handler.SendMessage(msg);
        }
    }
}

ToastHandler is just a simple handler that creates a toast. I know for a fact it works, because the message "Connecting..." appears on screen. The second message, however, doesn't appear. It seems that the client refuses to connect.

Any idea how to fix it?