Bad request in service

[OperationContract]
        [WebInvoke(Method = "POST", BodyStyle = WebMessageBodyStyle.Wrapped, RequestFormat = WebMessageFormat.Json, ResponseFormat = WebMessageFormat.Json, UriTemplate = "/GenerateMetadata/{FacilityID}")]
        public List<dynamic> GenerateMetadata(string FacilityID)
        {

var endpoint = String.Format("http://localhost/blahblah.svc/GenerateMetadata/FacilityID={0}", "555");
            var client = new RestClient(endpoint);
            var request = new RestRequest(endpoint, Method.POST);
            request.RequestFormat = DataFormat.Json;
            var response = client.Execute(request);
            dynamic data = JsonConvert.DeserializeObject<dynamic>(response.Content);