Getting 404 page not found when POSTing own page?

this is the code

[insert_php]
echo 'We have got: ' . $_POST['name'] . '';
[/insert_php]

AND

var txt = document.getElementById("name");
var send = txt.options[txt.selectedIndex].text;
 jQuery("button").click(function(){
    jQuery.post(" ",
    {
        name: send,
    },
    function(data, status){
        alert("Data: " + data + "\nStatus: " + status);
    });
})};

my goal is to have a small php short code handle the POST request INSIDE its own page.

i keep getting 404 error page not found https://www.myurl.com/wp/index.php/test_page

thanks

EDIT: i have also tryied hardcoding the url of my test site same thing 404 error