Google Calendar API Freebusy JQuery $ .post gets error 400 (failed request)

I am new to javascript, JQuery and Google API, so the answer to this question might be a very simple thing that I am missing. I have checked all the available Google Calendar Freebusy questions on this site, but I am unable to customize their answers in any way.

I am trying to write a script for an html page that checks an open free calendar request. Google states that the HTTP request should be

POST https://www.googleapis.com/calendar/v3/freeBusy

      

        
        
        
      

    

with request body

{
  "timeMin": datetime,
  "timeMax": datetime,
  "timeZone": string,
  "groupExpansionMax": integer,
  "calendarExpansionMax": integer,
  "items": [
    {
      "id": string
    }
  ]
}

      

        
        
        
      

    

My current html page has the latest jquery library and script I'm writing. Calling the script on the page results in an error Failed to load resource: the server responded with a status of 400 (Bad Request)

. Additional error information returns a parse error with"This API does not support parsing form-encoded input."

My script looks like this:

(function ($) {
  $.GoogleCalendarFreebusy = function (options) {
    var defaults = {
      apiKey: '[projectkey]',
      getID: '[id]@group.calendar.google.com',
      element: '#div'
    };

    options = $.extend(defaults, options);

    $.post('https://www.googleapis.com/calendar/v3/freeBusy?key=' + options.apiKey,
           {"items":[{"id": getID }],"timeMin":"2015-04-10T14:15:00.000Z","timeMax":"2015-04-20T23:30:00.000Z"}, "null", "json")    
    .done(function(data) {
        loaded(data);
      });

    function loaded(data) {
      var status = data.calendars[getID].busy;

      console.log(status);

      if(status.length !== 0 ) {

      for(var i = 0; i < status.length; i++) {
        var statusEntry = status[i];
        var startTime = statusEntry.start;
        var endTime = statusEntry.end;
      }

        var now = new Date().toISOString();
        var element = options.element ;
        var name = element.substr(1);

        if (now > startTime && now < endTime){

             $(options.element).append( 'Available!');

        }

        else {

            $(options.element).append( 'Unavailable!');

            }

    } else {

    $(options.element).append('Unavailable!');

    }

    }

  };
})(jQuery);

      

        
        
        
      

    

My request is getting the correct response in Google Explorer "Try it" , so I think it might be a javascript / json request error I "Skip?" Thanks in advance for your help and advice.