c# Asana POST新任务返回错误400(错误请求)

我有一个问题，在Asana从我的应用程序创建新的任务。

Post方法:

protected static T Post<T>(string route, object action = null, object parameters = null) where T : BaseResult, new()
    {
        var result = new T();
        try
        {
            var actionUrl             = GetActionUrl(route, action);
            var request               = (HttpWebRequest)WebRequest.Create(actionUrl);
            request.Credentials       = CredentialCache.DefaultCredentials;
            request.Accept            = "application/json";
            request.Method            = WebRequestMethods.Http.Post;
            request.Proxy.Credentials = CredentialCache.DefaultCredentials;
            request.Headers.Add("Authorization: Bearer " + ApiKey);
            if (parameters != null)
            {
                var contentJSON       = JsonConvert.SerializeObject(parameters);
                request.ContentType   = "application/json";
                using (var s = request.GetRequestStream())
                    using (var sw = new StreamWriter(s, Encoding.UTF8))
                        sw.Write(contentJSON);
            }
            var response = (HttpWebResponse) request.GetResponse();
            using (var reader = new StreamReader(response.GetResponseStream()))
            {
                var data = reader.ReadToEnd();
                result   = JsonConvert.DeserializeObject<T>(data);
            }
        }
        catch (Exception ex)
        {
            result.IsOk    = false;
            result.Message = ex.GetMessage();
        }
        return result;
    }

动作URL: https://app.asana.com/api/1.0/workspaces/MyWorkspace/tasksJSON: {"data":{"name":"TestTask1","notes":"Test note","workspace":"*MyWorkspace*","assignee":"*MyAssignee"}}

但是Asana返回给我"远程服务器返回了一个错误:(400)错误的请求。"

如果我更改请求。内容类型到"application/x-www-form-urlencoded"，我没有得到错误，但是Asana返回给我一个空字段的新任务。

我接下来要解决的问题应该是什么?

谢谢