在ajax中设置绝对路径不起作用

I am trying to set the absolute path to the url so that it loads from domain.com/functions/contact.php, but when I do so I get a 500 server status error

$.ajax({
        url: "/functions/contact.php",
        type: "post",
        data: {stage : optionScope.data().stage,
              topics: optionScope.data().topic,
              mentor: optionScope.data().mentor,
              fname: $('#fname').val(),
              email: $('#email').val(),
              humancheck: $('#humancheck').val()
            },
        success: function (response) {
            console.log("data sent successfully");
            window.location = response;

        },
        error: function (xhr, desc, err) {
            console.log(xhr);
            console.log("Details: " + desc + "
Error:" + err);
        }
    });