406-Not Acceptable Response in HTTP

HTTP Error 406 is usually returned when the requested file exists but cannot be used as the client system doesn’t understand the format of the return response. Your backend service is saying that the response type it is returning is not provided in the Accept HTTP header in your Client request. Add the accept header to resolve the error. 

let headerObj = {
      "Authorization": 'Bearer '+accessToken,
      "Content-Type": "application/json",
      "Accept" : "*/*"
  };