Problem with sending ajax request

I have a form. It sends data to php-script. But I would like to add on click event to send ajax request to another page (in addition to the main form action). So when I click submit button, ajax sends. It returns alert (in 'done' section), but PHP-handler at /payment page is not working as expected (it works perfectly if i just send ajax request without sending standard from action). Can anybody help to resolve this issue? This is my js:

$( "#place_btn" ).click(function() { if($('#payment').is(':checked')) { var x = 1; $.ajax({ method: "POST", url: "/payment", data: { var_x: x } }) .done(function() { alert("aaa"); }); }; });

And this is in relation to which component/module?