会话开始重定向不起作用

Question

I add this code to my php page:

<?php 
session_start();
if(!isset($_SESSION['username'])){
header('Location: login.php');
}

?>

As I said it`s on top of my page but redirect does not work I have got a message in browser "we can't reach this page."

Answer 1

<?php 
session_start();
if(!isset($_SESSION['username'])){
echo "Session exist"; exit;
}
else{
echo "No Session Found"; exit;
}
?>

This will Verify there is session or not