This is an example of how the endpoint file looked like. This was set to capture the data SendGrid's webhook was sending.

endpoint_file.php

<?php
date_default_timezone_set('America/New_York');
ini_set('display_errors', 1);
ini_set('display_startup_errors', 1);
error_reporting(E_ALL);

$myFile = "tmp/log.txt";
$fh = fopen($myFile, 'a+') or die("can't open file");

	if ($fh){
	    $headers = apache_request_headers();
	    $postdata = file_get_contents("php://input");

		foreach ($headers as $header => $value) {
		    fwrite($fh, print_r("$header: $value \n", true));
		}

		fwrite($fh, print_r($postdata, true));
		fclose($fh);
	}
?>