400 Response REST API Creating Blog when using PostImageFileUploadContext

Then I would make sure you are actually uploading the image correctly

How can we confirm that?

This is the data we are getting from the upload repost:

{{
  "UploadedFile": {
    "UploadContextId": "5bb07d0a-dbc9-489b-97fc-f08609d446cc",
    "DownloadUrl": "http://localhost/cfs-file/__key/CommunityServer-Components-MultipleUploadFileManager/5bb07d0a_2D00_dbc9_2D00_489b_2D00_97fc_2D00_f08609d446cc-2100-complete/Gruppenfoto_5F00_3_5F00_komprimiert_2D00_1.jpg",
    "TotalChunks": 1,
    "CurrentChunk": 0,
    "FileName": "Gruppenfoto_3_komprimiert-1.jpg"
  },
  "Errors": null
}}

This is the code we are using to upload the file:

  // Create request
                        var request = (HttpWebRequest)WebRequest.Create(url + "/api.ashx/v2/cfs/temporary.json");
                        request.Headers.Add("Rest-User-Token", restUserToken);
                        request.ContentType = "multipart/form-data; boundary=" + boundary;

                        // Collect necessary request information
                        var formData = new Dictionary<string, string>
                    {
                        {"UploadContextId", uploadContextId.ToString()},
                        {"FileName", fileName},
                        {"CurrentChunk", currentChunk.ToString()},
                        {"TotalChunks", totalChunks.ToString()},
                    };

                        // Add data to the multi-part form
                        var requestData = new StringBuilder();
                        foreach (var item in formData)
                        {
                            requestData.Append($"--{boundary}\r\nContent-Disposition: form-data; name=\"{item.Key}\"\r\n\r\n{item.Value}\r\n");
                        }

                        // Add the file itself
                        requestData.Append($"--{boundary}\r\nContent-Disposition: form-data; name=\"file\"; filename=\"{fileName}\"\r\nContent-Type: {fileContentType}\r\n\r\n");

                        // Prepare data chunk
                        var startDataBytes = Encoding.UTF8.GetBytes(requestData.ToString());
                        var chunk = rdr.ReadBytes(MAX_CHUNK_SIZE_BYTES);
                        var endDataBytes = Encoding.UTF8.GetBytes($"\r\n--{boundary}--\r\n");

                        // Combine all the request data into one array
                        var bytesToSend = new byte[startDataBytes.Length + chunk.Length + endDataBytes.Length];
                        startDataBytes.CopyTo(bytesToSend, 0);
                        chunk.CopyTo(bytesToSend, startDataBytes.Length);
                        endDataBytes.CopyTo(bytesToSend, startDataBytes.Length + chunk.Length);

                        try
                        {
                            // Make request and read results
                            var response = SendPostRequest(request, bytesToSend);
                            if (response?["Errors"] != null)
                            {
                                return string.Join("\r\n", response["Errors"]);
                            }
                            return response;
                        }
                        catch (Exception ex)
                        {
                            return InvestigateError(ex);
                        }

We are seeing this error in our exceptions from trying to load the image: