To remove a cookie, set the expiry timestamp to a time in the past. This triggers the browser's removal mechanism:
setcookie('user', '', time() - 3600, '/');
When deleting a cookie make sure the
setcookie()matches the cookie you're trying to delete or a new cookie, which expires immediately, will be created.
It is also a good idea to unset the
$_COOKIE value in case the current page uses it: