I am trying to upload attachment from user to Bot, I tried to write the code as straight forward and test it on Microsoft Bot Emulator. the problem is I am getting error (Send failed) POST 400 directline/conversations//upload

This is the code I am using.

public class AttachmentsBot : ActivityHandler
{
private readonly IHttpClientFactory _httpClientFactory;

 public AttachmentsBot(IHttpClientFactory httpClientFactory)
 {
     _httpClientFactory = httpClientFactory;
 }

 protected override async Task OnMessageActivityAsync(ITurnContext<IMessageActivity> turnContext, CancellationToken cancellationToken)
 {
     var attachments = turnContext.Activity.Attachments;
     if (attachments != null && attachments.Count > 0)
     {
         foreach (var attachment in attachments)
         {
             await ProcessAttachmentAsync(turnContext, attachment, cancellationToken);
         }
     }
     else
     {
         await turnContext.SendActivityAsync(MessageFactory.Text("Please attach a file."), cancellationToken);
     }
 }

 private async Task ProcessAttachmentAsync(ITurnContext turnContext, Attachment attachment, CancellationToken cancellationToken)
 {
     var client = _httpClientFactory.CreateClient();

     try
     {
         // Log the ContentUrl for debugging purposes
         Console.WriteLine($"Attachment URL: {attachment.ContentUrl}");

         // Download the file from the given ContentUrl
         var response = await client.GetAsync(attachment.ContentUrl, cancellationToken);
         if (response.IsSuccessStatusCode)
         {
             var fileBytes = await response.Content.ReadAsByteArrayAsync(cancellationToken);
             var fileName = attachment.Name ?? "unknown";
             var contentType = attachment.ContentType;

             // Save the file locally (for example purposes)
             var filePath = Path.Combine(Path.GetTempPath(), fileName);
             await File.WriteAllBytesAsync(filePath, fileBytes, cancellationToken);

             // Respond to the user
             await turnContext.SendActivityAsync(
                 MessageFactory.Text($"Attachment '{fileName}' of type '{contentType}' has been saved to {filePath}."),
                 cancellationToken);
         }
         else
         {
             // Log the error response
             Console.WriteLine($"Failed to download attachment. HTTP Status: {response.StatusCode}");
             await turnContext.SendActivityAsync(
                 MessageFactory.Text($"Failed to download attachment: {attachment.Name}. HTTP Status: {response.StatusCode}"),
                 cancellationToken);
         }
     }
     catch (Exception ex)
     {
         await turnContext.SendActivityAsync(
             MessageFactory.Text($"An error occurred while processing the attachment: {ex.Message}"),
             cancellationToken);
     }
 }

}

I expect to get the attachment and process it in the code.