PHP Ajax 404 Not Found error

Question

I'm newer to web development and I'm working on a small project for myself and some friends as a hobby. I've not touched PHP before this so I'm well aware that what you're about to see is garbage. The problem is that I don't even know if my code is good because I can't get it to run on my site.

Here's my javascript/ajax:

$.ajax({
    type : "POST",
    url : "/some.php",
    data : {
    json : JSON.stringify(data)
    }
});

And here's my some.php file:

<?php
$myFile = "json/your_array.json";
$fh = fopen($myFile, 'w') or die("impossible to open file");
$stringData = $_POST['data'];
fwrite($fh, $stringData);
fclose($fh);
?>

Again, I'm well aware that what you're looking at is garbage, but I just need it to read the php file in the first place. I made a post for help with the code itself once before but I didn't get much help there.

The error I get in the web console just says 404 not found. Anyone have an idea?