Web Service method name isn't valid

I have tried lots of solution but my problem isn't solved. What is the problem in this code omg.

I am posting this with fiddler :

{"No":1,"Name":"sss","LastName":"ssss","Age":1}

User Class:

 public class Users
{
    public Users() { }
    public Users(int no,string name,string lastname, int age)
    {
        this.No = no;
        this.Name = name;
        this.LastName = lastname;
        this.Age = age;
    }
    public int No { get; set; }
    public string Name { get; set; }
    public string LastName { get; set; }
    public int Age { get; set; }
}

Webmethod :

[WebMethod]
    public void updateUser(Users usr)
    {
        Users temp = userList.Where(i => i.No == usr.No).FirstOrDefault();
        userList.Remove(temp);
        userList.Add(usr);
    }

This is the error :

{"Message":"Invalid web service call, missing value for parameter: \u0027usr\u0027.","StackTrace":"   at System.Web.Script.Services.WebServiceMethodData.CallMethod(Object target, IDictionary`2 parameters)\r\n   at System.Web.Script.Services.WebServiceMethodData.CallMethodFromRawParams(Object target, IDictionary`2 parameters)\r\n   at System.Web.Script.Services.RestHandler.InvokeMethod(HttpContext context, WebServiceMethodData methodData, IDictionary`2 rawParams)\r\n   at System.Web.Script.Services.RestHandler.ExecuteWebServiceCall(HttpContext context, WebServiceMethodData methodData)","ExceptionType":"System.InvalidOperationException"}