php alert does not work when redirect to another page with session variable

Question

I need to prevent access to " http://localhost/oms/category/index.php " page where $_SESSION['role'] is not equal 'Administrator' or 'Operator'. so when an user with another role (not admin or operator) try to access to above page, user is redirected to another page. it's ok. but alert message is not work. how can i fix this.

code in localhost/oms/category/index.php is here

session_start();
if (!isset($_SESSION['username'])) {
header('Location: ../login/index.php');
}
if (!($_SESSION['role'] == 'Administrator' || $_SESSION['role'] == 
'Operator')) {
$_SESSION['alert-warning'] = "You do not have permission to access the 
page.";
header('Location: ../customer-order/');
}

code in redirected page is here

<?php
session_start();
if (isset($_SESSION['alert-success'])) {
?>
<div class="alert alert-success" id="success-alert" role="alert" data-auto- 
dismiss="2000">
    <button type="button" class="close" data-dismiss="alert">x</button>
    <strong>Success! </strong>
    <?php echo $_SESSION['alert-success']; ?>
</div>
<?php
unset($_SESSION["alert-success"]);
} else if (isset($_SESSION['alert-unsuccess'])) {
?>    
<div class="alert alert-danger" id="unsuccess-alert">
    <button type="button" class="close" data-dismiss="alert">x</button>
    <strong>Error&nbsp;!&nbsp;&nbsp; </strong>
    <?php echo $_SESSION['alert-unsuccess']; ?>
</div>
<?php
unset($_SESSION["alert-unsuccess"]);
} else if (isset($_SESSION['alert-warning'])) {
?>
<div class="alert alert-warning" id="success-alert" role="alert" data-auto- 
dismiss="2000">
    <button type="button" class="close" data-dismiss="alert">x</button>
    <strong>Warning! </strong>
    <?php echo $_SESSION['alert-warning']; ?>
</div>
<?php
unset($_SESSION["alert-warning"]);
}
?>

Answer 1

Your || statement is always false, switch it to:

if (!($_SESSION['role'] == 'Administrator' && $_SESSION['role'] == 'Operator'))