getting json in flask from jquery ajax

I need some help with getting json data in flask from jquery ajax.

Below client side javascript which gets called whenever some button is clicked.

<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js"></script>
<script>
    function change_status(item, status) {
          var statusObj={"desc":item, "status":status};
          $.ajax({
                    url:"/robot/api/"+item,
                    type: "PUT",
                    contentType:"applicaton/json",
                    dataType:"json",
                    data: JSON.stringify(statusObj)
          });
    }
</script>

on server side(flask), I have below code to catch json data.

@app.route('/robot/api/<item>', methods = ['PUT'])
def update_item(item):

print "content_type: ", request.content_type

print "request.json: ", request.json

if not request.json:
    print "bad json format"
    abort(400)
else
    """
    do something like update data
    """

In PC, when clicking button in the browser which calls javascript function, flask server is printing below message:

"content_type:  applicaton/json; charset=UTF-8

request.json:  None

bad json format

192.168.1.241 - - [12/Feb/2014 15:06:16] "PUT /robot/api/3g HTTP/1.1" 400 -"

It shows request.content_type is json but when actually printed it says None.

I did packet capture to see data from PC with wireshark and I see below:

From PC to Flask Server:

PUT /robot/api/3g HTTP/1.1

Host: "my flask server ip address"

User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:26.0) Gecko/20100101 Firefox/26.0

Accept: application/json, text/javascript, */*; q=0.01

Accept-Language: en-US,en;q=0.5

Accept-Encoding: gzip, deflate

Content-Type: applicaton/json; charset=UTF-8

X-Requested-With: XMLHttpRequest

Referer: "my flask server ip address"

Content-Length: 28

Connection: keep-alive

{"desc":"3g","status":"off"}

But Flask server returns "HTTP/1.0 400 BAD REQUEST"