Accessing CI session data outside of CI

I have a folder in my

Code:

Codeigniter4/public/oldproject

where i have created a test.php so that I can access it using

PHP Code:

myci4site.com/oldproject/test.php 


In test.php

PHP Code:

$path = realpath(dirname(dirname(dirname(__FILE__))).'/writable/session');
//ini_set('session.save_path',$path);
session_save_path ($path);
session_id( $_COOKIE['ci4session'] );
session_start();

print_r($_SESSION); 


but it prints an empty array.

There is session data in the session which I can print in my Home controller e.g. myci4site.com/home/test which just contains

PHP Code:

$sess = session()->get();
echo '<pre>';print_r($sess); 


What else I need to do to be able to get session data in my test.php?

I need to access this data for maintaining old code for the time being.
Thanks.