Working PayPal IPN script

ipn-endpoint.php

<?php

  require_once 'PaypalIPN.php'; // from https://github.com/paypal/ipn-code-samples/blob/master/php/PaypalIPN.php
  
  $env = 'sandbox'; // set somewhere else normally

  $ipn = new PaypalIPN();
  if ($env == 'sandbox') { 
    $ipn->useSandbox(); // use sandbox endpoint to verify
    $ipn->usePHPCerts(); // use local certs for testing
  }
  $verified = $ipn->verifyIPN();

  $paypal_ipn_status = "VERIFICATION FAILED";
  if ($verified) { // verified
    $paypal_ipn_status = "VERIFIED";
    
    /* do something */
  } elseif ($env == 'sandbox') {
    if ($_POST["test_ipn"] != 1) {
      $paypal_ipn_status = "RECEIVED FROM LIVE WHILE SANDBOXED";
    }
  } elseif ($env == 1) {
    $paypal_ipn_status = "RECEIVED FROM SANDBOX WHILE LIVE";
  }

  if ($env == 'sandbox') {
    /* logging */
  }

// Reply with an empty 200 response to indicate to paypal the IPN was received correctly
  header("HTTP/1.1 200 OK");