post method not working with angular js and asmx page

i have created web service using asmx page in which has a method

[WebMethod]

public string InsertStudent(string Name, string Gender, string City)

{

operation oper = new operation();

string query = string.Empty;

try

{

oper.Trans_Begin();

query = @"SELECT MAX(ID)+1 AS ID FROM TBLSTUDENTS";

int id = Convert.ToInt32(oper.DTSET(query).Tables[0].Rows[0]["ID"].ToString());

query = string.Empty;

query = @"INSERT INTO TBLSTUDENTS VALUES('" + id + "','" + Name + "','" + Gender + "','" + City + "')";

oper.sqinsert(query);

oper.Trans_Commit();

return query;

}

catch(Exception ex)

{

oper.Trans_Rollback();

return "error";

}

my angular code is

$scope.Save = function () {

let name=$scope.studentname,gender=$scope.studentgender,city=$scope.studentcity;

let datalist=JSON.stringify({Name:name,Gender:gender,City:city});

$http({

url: "Student.asmx/InsertStudent",

method: "post",

headers: {

"Content-Type": "application/json; charset=utf-8",

"dataType": "json"

data: datalist

}).then(function (response) {

$scope.message = "Saved Sucessfully";

}), function (reason) {

$scope.message = reason.data;

}

i am getting internal server error please help

here is the example

https://groups.google.com/forum/#!topic/firebase-angular/6wLh5oAnpak

for my problem