Unable to download Image from URL Xamarin Form

I am developing a Xamarin app which retrives info from DB, take/choose photo and upload them to remote server, display this images from the remote server and the user can delete them by tap on and press a button. The final step is to download the images stored in the server to the local device gallery.

This is my current button click event:

private void button_download_image_Clicked(object sender, EventArgs e)
{
        Uri image_url_format = new Uri(image_url);
        WebClient webClient = new WebClient();
        try
        {              
            webClient.DownloadDataAsync(image_url_format);
            webClient.DownloadDataCompleted += webClient_DownloadDataCompleted;
        }
        catch (Exception ex)
        {
            DisplayAlert("Error", ex.ToString(), "OK");
        }
}

Below the webClient_DownloadDataCompleted method:

private void webClient_DownloadDataCompleted(object sender, DownloadDataCompletedEventArgs e)
{
    try
    {
        Uri image_url_format = new Uri(image_url);
        byte[] bytes_image = e.Result;
        Stream image_stream = new MemoryStream(bytes_image);
        string dest_folder= Android.OS.Environment.GetExternalStoragePublicDirectory(Android.OS.Environment.DirectoryDownloads).ToString();
        string file_name= Path.GetFileName(image_url_format.LocalPath);
        string dest_path= Path.Combine(dest_folder, file_name);
        using (var fileStream = new FileStream(dest_path, FileMode.Create, FileAccess.Write))
        {
              image_stream.CopyTo(fileStream);
        }
              DisplayAlert("Alert", "Download completed!", "OK");
        }
        catch (Exception ex)
        {
            DisplayAlert("Error", ex.ToString(), "OK");
        }
    }

But it does not work, no error caught, I get the alert which warn me that the download is completed. Also I gave permission for internet, write_external_storage and read_external_storage.

Another thing is that the images after some time, appears in the gallery under Download album which is correct.

Any idea about this behavior?