Recieving 303 Error Code in external script Moodle

Question

I have written an external script to update user data in moodle. I included moodle/onfig.php file in the external script. When I access the external script I receive 303 error and redirected to dashboard page, I cannot share the code.

<?php
  require_once('../config.php');
  if (!empty($CFG->forcelogin) or !isloggedin()) {
     echo "<a href='$CFG->wwwroot/login/' target='_blank'>you are not logged in.</a><br/>";
     exit();
  }
?>

when I comment the require_once('../config.php'); the script is working fine. But I need the config file to update users data.