Ajax Call not happening for WebMethod

I am trying to call a WebMethod using a function that contains Ajax Call request.But it is giving Internal Server error 500.Here is the function that contains the Ajax ..

function ajaxCall(URL) {

var serverData = "";

$.ajax({
    url: URL,
    dataType: 'json',
    contentType: "application/json; charset=utf-8",
    type: 'POST',
    success: function (queriedData, textStatus, XMLHttpRequest) {
        serverData = queriedData;
    },
    error: function (request, status, error) {
        alert(error);
    }
});
return serverData;
}

and Here i am trying to Call this jquery function ..

 var checkInBookingIDData = ajaxCall(URL);

and Here is the URL value that i am trying to pass..

http://ift.tt/1HF80xY

I am not able to find out where i am going wrong .Please help me ..Thanks..