ASP.NET + jQuery AJAX - getting 500 server error

Question

I want to call an ASP.NET function from jQuery by AJAX with response.

I have file Controll.aspx where is included javascript code. Next I have /Services/ControllService.asmx, where is the function, which I want call from js.

js code:

$(document).ready(function () {
    $('#btn_start').on('click', function () {
        $.ajax({
            type: "POST",
            url: "Services/ControllService.asmx/Start",
            data: {},
            dataType: "json",
            async: true,
            contentType: "application/json; charset=utf-8",
            success: function (response) {
                console.log(response);
            },
            error: function (err) {
                alert("Error:" + err.toString());
            }
        });

    });
});

But I still getting the error 500.

POST http://localhost:56000/Services/ControllService.asmx/Start 500 (Internal Server Error)
k.cors.a.crossDomain.send
n.extend.ajax

Do you have any hints, what do I need to set eg in Web.config?

Many thanks.

Answer 1

SOLVED:

1 - I have defined Start function in ControllService.asmx.cs as static.

2 - I have badly configured data. It has to be named by the same way eg "sth".

In javascript it should be:

...
url: "Services/ControllService.asmx/Start",
data: JSON.stringify({ sth: "hahaha" }),
dataType: "json",
...

and in ControllService.asmx.cs -> method Start

public string Start(string sth){}

Many, many thanks for your hints.