[Activity(Label = "xam.paypal.test", MainLauncher = true, Icon = "@mipmap/icon")]
public class MainActivity : Activity
{
  private PayPalConfiguration config = new PayPalConfiguration()
      .Environment(PayPalConfiguration.EnvironmentSandbox)
      .ClientId("YOUR CLIENT ID HERE");

protected override void OnCreate(Bundle savedInstanceState)
{
    base.OnCreate(savedInstanceState);

    // Set our view from the "main" layout resource
    SetContentView(Resource.Layout.Main);

    // Get our button from the layout resource,
    // and attach an event to it
    Button button = FindViewById<Button>(Resource.Id.myButton);
    button.Click += this.ButtonOnClick;

    // start paypal service
    var intent = new Intent(this, typeof(PayPalService));
    intent.PutExtra(PayPalService.ExtraPaypalConfiguration, config);
    this.StartService(intent);
}

private void ButtonOnClick(object sender, EventArgs eventArgs)
{
    var payment = new PayPalPayment(new BigDecimal("2.45"), "USD", "the item",
        PayPalPayment.PaymentIntentSale);

    var intent = new Intent(this, typeof(PaymentActivity));
    intent.PutExtra(PayPalService.ExtraPaypalConfiguration, config);
    intent.PutExtra(PaymentActivity.ExtraPayment, payment);

    this.StartActivityForResult(intent, 0);
}

protected override void OnActivityResult(int requestCode, Result resultCode, Intent data)
{
    if (resultCode == Result.Ok)
    {
        var confirm = data.GetParcelableExtra(PaymentActivity.ExtraResultConfirmation);
        if (confirm != null)
        {
            try
            {
                Log.Info("xam.paypal.test", confirm.ToString());

                // TODO: send 'confirm' to your server for verification.
                // see https://developer.paypal.com/webapps/developer/docs/integration/mobile/verify-mobile-payment/
                // for more details.

            }
            catch (JSONException e)
            {
                Log.Error("xam.paypal.test", "something wen really wrong here: ", e);
            }
        }
    }
    else if (resultCode == Result.Canceled)
    {
        Log.Info("xam.paypal.test", "Canceled.");
    }
    else if ((int)resultCode == PaymentActivity.ResultExtrasInvalid)
    {
        Log.Info("xam.paypal.test", "Invalid Payment or PayPalConfiguration.");
    }
}


protected override void OnDestroy()
{
    this.StopService(new Intent(this, typeof(PayPalService)));
    base.OnDestroy();
}