Insert php

I can’t make this code work in my Avada Theme.
I placed it in the top of the page, to block out users who hasn’t been througt login.
Can anyone help?

[insert_php]
session_start();

// Check to see if the user has been through the login process
if (! isset($_SESSION[‘USER_ID’]) or ! isset($_SESSION[‘LICENSES_GRANTED’])) {
// The user arrived here without being logged in so relocate to the front page
header(“Location: /index.htm”);
}
[/insert_php]