Notification Creation Issue using Remote API

Hi,

Please find that, i am trying to create "Excess Idling"  notification using Remote API. I am following below format and its getting created properly if i am using tool like "PostMan" for creating post request. But the same format does not work if we are using (HTTpClient in C#) .

It returns error code 4 which is for invalid input.

Can you please have a look and suggest if we are missing anything while formatting the parameters.

{ 
   "n":"Test Excess Idling Notification",
   "ta":1492598264,
   "td":0,
   "tz":-18000,
   "la":"en",
   "ma":0,
   "sch":{ 
      "f1":0,
      "f2":0,
      "t1":0,
      "t2":0,
      "m":0,
      "y":0,
      "w":0,
      "fl":0
   },
   "un":[ 
      XXXXX
   ],
   "trg":{ 
      "t":"speed",
      "p":{ 
         "sensor_type":"engine operation",
         "sensor_name_mask":"*Ignition*",
         "lower_bound":"0",
         "upper_bound":"0",
         "prev_msg_diff":"0",
         "merge":"0",
         "reversed":"1",
         "min_speed":"2",
         "max_speed":"10000",
         "min_idle_time":"15"
      }
   },
   "act":[ 
      { 
         "t":"event",
         "p":{ 
            "flags":"1"
         }
      }
   ],
   "txt":"Dear Valued Customer,",
   "fl":0,
   "mast":0,
   "mpst":0,
   "cdt":0,
   "mmtd":180,
   "cp":0,
   "id":0,
   "itemId":YYYYY,
   "callMode":"create"
}