Parse error: syntax error, unexpected '? ' tell me ans

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PHP

Parse error: syntax error, unexpected '?' in C:\xampp\htdocs\pharmacy_Management_System\index.php on line 3
kindly resolve this problem

What I have tried:

<pre><?php
    session_start();
    $sessionId = $_SESSION['id'] ?? '';
    $sessionRole = $_SESSION['role'] ?? '';
    echo "$sessionId $sessionRole";
    if ( !$sessionId && !$sessionRole ) {
        header( "location:login.php" );
        die();
    }

    ob_start();

    include_once "config.php";
    $connection = mysqli_connect( DB_HOST, DB_USER, DB_PASSWORD, DB_NAME );
    if ( !$connection ) {
        echo mysqli_error( $connection );
        throw new Exception( "Database cannot Connect" );
    }

    $id = $_REQUEST['id'] ?? 'dashboard';
    $action = $_REQUEST['action'] ?? '';
?>