400 Response REST API Creating Blog when using PostImageFileUploadContext

Are you evaluating the actual responses to get the error?  Also again, please do not use the SDK.  You cannot use it for file uploading which this requires as the post image url  context is the string used when uploading the actual image.  Second, you provided the string, but no PostImageFileName.

I have stated this in previous threads as well, you do not concatenate data into a url.  Blog Id is a Path Parameter, you set the url to /blogs/{blogid}/posts.xml  then define blogid as a path parameter

I am uploading the images outside of the SDK. I am just using it here for ease of use.

I tired using {blogid} instead of the int value and it was throwing errors so i went back to passing in the INT.

Implementing your suggestions I am still getting the same errors:

Did you look at the response for the error?

Its showing as "Not Found"

Did you actually create and set blogid  is PathParameters collection?  NOT PostParameters

Ah ha, progress. Now the post is posting and the Image URL but the image is returning a 400 error.

Request:

Ah ha, progress. Now the post is posting and the Image URL but the image is returning a 400 error.

Request:

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: 

Did you go and verify the file integrity in the filestorage to make sure you uploaded correctly?

Where do files get uploaded?