注销链接不起作用PHP

I'm trying to use a logout link to logout from a form, but it's not working (error appears). What am I doing wrong?

Logout.php code:

<? php
session_start(); 
session_unset();
session_destroy();
header('Location: Login Link');
exit;

?>

Login Form:

<?php
session_start();
?>

<?php
(...)
echo' <p style="text-align:left;"> <a href="abc/logout.php">Logout</a> </p>';

(...)
?>

You made a typo mistake:

<? php --> <?php

your first line is <? php and it should be <?php, notice the space