使用C＃的Dropbox文件下载错误路径/未找到

Question

我想使用C＃从Dropbox下载文件，我使用以下代码：

 async void Download(string Folder_Name, string DropBox_File_Name)
    {
        DropboxClient client = new DropboxClient("XXXXXXXXXXXXXXXXXXXXXXXXX");
        try
        {
            string path =  Folder_Name + "/" + DropBox_File_Name;
            using (var download = await client.Files.DownloadAsync(path))
            {

                using (var fileStream = File.Create(Application.StartupPath+"\\"+DropBox_File_Name))
                {
                    (await download.GetContentAsStreamAsync()).CopyTo(fileStream);
                }
            }
        }
        catch (DropboxException ex) { Console.WriteLine(ex.Message); }
    }
      private void button1_Click(object sender, EventArgs e)
    {

     Download("/Apps/Retailme", "Sale Book.pdf");

    }

但是这给出了错误路径/ not_found 该如何解决？