POST请求上的Ajax 403

Question

I am using a jQuery image cropper. When an image is cropped and a button is pressed to send it to the file via ajax (as seen below) I get a 403 Forbidden error.

$('body').on("click", '.saveimage', function () {
    $.ajax({
        type: "post",
        url: "save.php",
        data: foo.crop(200, 200, 'png')
    }).done(function(data) {
    });
});

I am not using the Django framework and I'm trying to look for answers but all I seem to find are Django or Tornado answers. This is save.php:

<?php
    if ($_SERVER['REQUEST_METHOD'] == "POST") 
    {
        $img = str_replace('data:image/'.$_POST['type'].';base64,', '', $_POST['string']);
        $img = str_replace(' ', '+', $img);

        // logic to determine file name
        $filename = 'smush';

        file_put_contents($filename . '.' . $_POST['type'], base64_decode($img));
    }
?>

No errors are being logged, I have not got any csrf implemented yet. All help is appreciated. If I'm missing something, let me know.