callback-collector.php

<?php
/*
  Place this file in writable directory. Each incoming request will be saved as a file.
  Sample file name:
    callback_POST_08-17-2022 13.42.05.780400.txt
*/

$now = DateTime::createFromFormat('U.u', microtime(true));

$file_name = 'callback_' . $_SERVER['REQUEST_METHOD'] . '_' . $now->format("m-d-Y H.i.s.u").'.txt';

$myfile = fopen($file_name, "w") or die("Unable to open file!");

fwrite($myfile, "GET:" . json_encode($_GET));
fwrite($myfile, "\nPOST:" . file_get_contents('php://input'));
fclose($myfile);