无法使用Jive REST API发布共享-收到400个错误请求

我正在尝试使用c#在。net中使用/Shares REST API在Jive上发布一个共享。然而，我无法做到这一点，并得到以下错误:

"远程服务器返回一个错误:(400)错误请求。"

下面是我写的代码:

string response = string.Empty;
using(WebClient client = new WebClient())
{
   string strJiveShareURL = "https://<JiveURL>";
          strJiveShareURL += "/api/core/v3/shares";
   var SharedJSON = new AddShareJSON
   {
      participants = new string[] {"https://<JiveURL>/api/core/v3/people/{username}" },
      shared = "https://<<Content URL to be shared>>",
      content= new Content
                {
                  type = "text/html",
                  text = "This is a test share from SharePoint to Jive"                   
                }
}; 
   var serializer = new System.Web.Script.Serialization.JavaScriptSerializer();
   string shareJSON = serializer.Serialize(SharedJSON);
   Console.WriteLine("Setting Credentials:");
   string credentials = Convert.ToBase64String(Encoding.ASCII.GetBytes("UID:PWD"));
   client.Headers[HttpRequestHeader.Authorization]= "Basic " + credentials;
   client.Headers[HttpRequestHeader.Accept] = "application/json";
   client.Headers[HttpRequestHeader.ContentType] = "application/json";
   //BypassCertificateError();
   response = client.UploadString(strJiveShareURL, "POST", shareJSON);
   Console.WriteLine("Response:" + response);
   Console.ReadLine();

}

，下面是为发布共享而创建的JSON:

{
  "content": {
                "type":"text/html",
                "text":"This is a test share from SharePoint to Jive"
            },
           "participants": ["https://<<Jive URL>>/api/core/v3/people/<<username>>"],
           "Shared":"https://<<URL of the Content To be Shared>>"
}

如果我做错了什么，请告诉我。