$user->set_cookie('poster', "123", time() + 120);
$rad3 = request_var($config['cookie_name'] . '_poster', '', false, true);
$user->set_cookie('poster2', $rad3, time() + 120);
Cookie results below:
phpbb3_9e25h_poster 123 localhost / 2019-06-07T16:44:47.010Z 22 ✓
phpbb3_9e25h_poster2 localhost / 2019-06-07T16:44:47.010Z 20 ✓
In the above I expected "123" in poster2 cookie.