Using REFIT throws an error when first time used, how to capture the exception

[dee-u]

First time to use Xamarin and I am trying to use a RESTful API for logging in, this code works but the first time I am clicking the BtnConnect it is throwing out an error and I am not sure how can I capture the error, I am using an android device connected thru USB, how can I capture or log the error?

private async void BtnConnect_Click(object sender, EventArgs e)
{
    try
    {
        txtUsername = FindViewById<TextView>(Resource.Id.txtUsername);
        txtPassword = FindViewById<TextView>(Resource.Id.txtPassword);

        string username = txtUsername.Text;
        string password = txtPassword.Text;
                
        var user = new UserModel
        {
            username = username,
            password = password
        };

        ApiResponse response = await ApiUtils.GetApiService().Login(user);

        Toast.MakeText(this, response.message, ToastLength.Long).Show();
    }
    catch (Exception ex)
    {
        Toast.MakeText(this, ex.StackTrace, ToastLength.Long).Show();

    }
}