PHP file not receiving postbacks

Hi. I've setup my postback url (currently: https://glowingstonewebsites.com/zerodha/orders) and I placed some orders through the API but I didn't receive any postbacks about the order updates. Here's the code in my PHP file:

<?php
$json = file_get_contents('php://input');
writeToLog("JSON: ".$json);

I've tested the URL through Postman and its working perfectly when I sent a sample payload. You can try sending one too, you should get an array back. How do I debug this? There seems to be no logs in the Kite Connect.