Got Inner exception: Error 12002 calling WINHTTP_CALLBACK_STATUS_REQUEST_ERROR, 'The operation timed out' using MS graph to send large attachment

Question

I use MS Graph API to send an email. I can send email with a small size attachment but I got an error when sending a large attachment:

Before progress after progressGeneral error uploading testFile.pdf: An error occurred while sending the request.
Inner exception: Error 12002 calling WINHTTP_CALLBACK_STATUS_REQUEST_ERROR, 'The operation timed out'. Email sent successfully

I set string to capture "Uploaded {prog} bytes of {totalLength} bytes" but it has nothing. I guess it may be upload issue.

Would you be able to give me a suggestion or example to solve this issue? Thanks in advance.

This is my code to create GraphServiceClient:

GraphServiceClient myGPClient = new GraphServiceClient(new ClientSecretCredential(tenantId, clientId, secretVal));

There is my code to attach the large attachment:

try
{
    string fileName = Path.GetFileName(largeAttachment);
    string contentType = GetMimeType(largeAttachment);

    // Add a small delay between attachment uploads
    await Task.Delay(1000);

    using (var fileStream = new FileStream(largeAttachment, FileMode.Open, FileAccess.Read))
    {
        var uploadbody = new Microsoft.Graph.Users.Item.Messages.Item.Attachments.CreateUploadSession.CreateUploadSessionPostRequestBody
        {
            AttachmentItem = new AttachmentItem
            {
                AttachmentType = AttachmentType.File,
                Name = fileName,
                Size = fileStream.Length,
                ContentType = contentType
            }
        };

        var uploadSession = await myGPClient.Users[emailUser]
                  .Messages[savedDraft.Id]
                  .Attachments
                  .CreateUploadSession
                  .PostAsync(uploadbody);

        if (uploadSession == null || string.IsNullOrEmpty(uploadSession.UploadUrl))
        {
            strErrorMsg += $"Failed to create upload session for {fileName}. Upload URL is null.{Environment.NewLine}";
            continue;
        }

        // Max slice size must be a multiple of 320 KiB
        int maxSliceSize = 320 * 1024 * 9;
        var fileUploadTask = new LargeFileUploadTask<FileAttachment>(uploadSession, fileStream, maxSliceSize);

        var totalLength = fileStream.Length;

        strErrorMsg += System.Environment.NewLine + "before progress";
        // Create a callback that is invoked after each slice is uploaded
        IProgress<long> progress = new Progress<long>(prog =>
            {
                //didn't have totalLength value on strErrorMsg
                strErrorMsg = strErrorMsg + System.Environment.NewLine + $"Uploaded {prog} bytes of {totalLength} bytes";
            });

        strErrorMsg += System.Environment.NewLine+ "after progress";

        // Upload the file
        var uploadResult = await fileUploadTask.UploadAsync(progress);

        if (!uploadResult.UploadSucceeded)
        {
            strErrorMsg = strErrorMsg + System.Environment.NewLine + $"Upload failed for file: {largeAttachment}";
        }
        else
        {
            strErrorMsg = strErrorMsg + System.Environment.NewLine + $"Successfully uploaded: {Path.GetFileName(largeAttachment)}";
        }
    }
}
catch (ServiceException ex)
{
    strErrorMsg += $"Service error uploading {Path.GetFileName(largeAttachment)}: {ex.Message}{Environment.NewLine}";

    if (ex.InnerException != null)
    {
        strErrorMsg += $"Inner exception: {ex.InnerException.Message}{Environment.NewLine}";
    }

    // Continue with the next attachment despite the error
    continue;
}
catch (Exception ex)
{
    strErrorMsg += $"General error uploading {Path.GetFileName(largeAttachment)}: {ex.Message}{Environment.NewLine}";

    if (ex.InnerException != null)
    {
        strErrorMsg += $"Inner exception: {ex.InnerException.Message}{Environment.NewLine}";
    }

    // Continue with the next attachment despite the error
    continue;
}

try
{
   // Send the draft
   await myGPClient.Users[emailUser].Messages[savedDraft.Id].Send.PostAsync();
   strErrorMsg += "Email sent successfully";
}
catch (ServiceException ex)
{
   strErrorMsg += $"Error sending email: {ex.Message}{Environment.NewLine}";
}