I’m trying to create a PHP forum page uses sessions. Every time I try to post a comment I keep getting the same error, not sure where I’m going wrong with this

Here’s my code for the form:

session_start();

if(!isset($_SESSION['user_id'])){

    require('login_tools.php');

    load();

    }

    $page_title = 'Post Message';

    include('includes/header.html');

    echo "

Home

        
You are now logged in, {$_SESSION['first_name']} 

{$_SESSION['last_name']}

        ";

    echo '
        
Subject: