Stringify Before POSTing

stringify

var data = { 
  name: "dave",
  age: 35,
  height: 188};
  
var submitData = JSON.stringify(data);

$.ajax({
  headers: { "X-RequestDigest": formDigestValue },
  url: url,
  method: "POST",
  contentType: "application/json",
  data: submitData,
  success: success,
  error: error
  });