php xhr request works on local but not on server

I've trying to create a progress bar while the script executes. It works fine when I test in Visual Studio, but when I put it on a server, it won't work. Is there some php or IIS setting that might be disabling this? It only fires at the end of the script execution. I've also tried multiple different ways of doing the XHR request. I've used xhrfields, xhr on it's own and ya... again works in development, but on the server, nope.

My php file

if ($_SERVER['REQUEST_METHOD'] == 'POST') {
    header('Content-Type: application/json');
    $response = array();
    $links = array();
    $progress = 0;
    $progressFinal = 10;
    echo json_encode(array('progress' => $progress));
    ob_implicit_flush(true);
    ob_end_flush();
    for($i = 0; $i < 10; $i++) {
        sleep(2);
        $progress++;
        echo json_encode(array('progress' => (round(($progress / $progressFinal) * 100))));
        flush();
        ob_flush();
    }
}

my js file

$.ajax({
        url: "test.php",
        type: 'POST',
    dataType: 'json',
        async: true,
        xhrFields:
        {
            onprogress: function (e) {
                var thisResponse, response = e.currentTarget.response;
                if (lastResponseLen === false) {
                    thisResponse = response;
                    lastResponseLen = response.length;
                }
                else {
                    thisResponse = response.substring(lastResponseLen);
                    lastResponseLen = response.length;
                }

                jsonResponse = JSON.parse(thisResponse);
                $('#emrcp').html('- ' + jsonResponse.progress + '%');
            }
        },
        success: function (text) {
            $('#emrcBtn').html('Sent!');
            for (var i = 0; i < response.links.length; i++) {
                $('#emlStat' + response.links[i].fam_id).html('Sent...');
            }
        }
    });

It happened to be my IIS settings like I figured. I just need to add responseBufferLimit="0" to my webconfig for php and FastCGI.