Sorry to bring back an old thread, but I'm just learning the platform and I thought I'd share my solution to this.

First, define a generic class to handle the raw json response data:
eg. my Tut1_AddTwoNumbers api returns:

{"data":{"response":{"answer":24},"success":true},"status":200}

    public class Response<T>
    {
        public ResponseData<T> data;
        public int status;
    }
    public class ResponseData<T>
    {
        public T response;
        public bool success;
    }

Then for each api call that you have, define a class that contains the fields that are custom to that response.

    public class Tut1_AddTwoNumbersResponse
    {
        public int answer;
    }

Now, you call your function and handle the response like this:

    public void Tut1_AddTwoNumbers()
    {
        string scriptName = "Tut1_AddTwoNumbers";
        // Anonymous object to supply the params.
        var data = new
        {
            num1 = 16,
            num2 = 8
        };

        var jsonScriptData = JsonWriter.Serialize(data);
        SuccessCallback successCallback = (response, userdata) =>
        {
            var responseObject = JsonReader.Deserialize<Response<Tut1_AddTwoNumbersResponse>>(response);
            //var responseObject = JObject.Parse(response);
            Debug.Log($"Success The answer is '{responseObject.data.response.answer}' | raw_json={response}");
        };
        FailureCallback failureCallback = (status, code, error, userdata) =>
        {
            Debug.Log(string.Format("Failed | {0}  {1}  {2}", status, code, error));
        };
        // Call the script 
        _bc.ScriptService.RunScript(scriptName, jsonScriptData, successCallback, failureCallback);
    }

this line is the important part:

JsonReader.Deserialize<Response<Tut1_AddTwoNumbersResponse>>(response);

Hope that helps someone!

Yes the data received is in JSON. And brainCloud expects a JSON when you update the entity. What you can do is create a serialize and a deserialize method inside your custom type.