Pretty Permalink Breaks sidebar PHP

I’m updating a legacy site for a client. It was a very old wordpress from 2009. A lot of the code is mixed with static and dynamic.

The sidebar changes with different pages depending on the page template.

This is the current side bar code

<div id=”sidebar”>
<?php
$pageID = $_GET[“page_id”];
$sidebar = get_post_meta($pageID, ‘sidebar’, true);

if(is_single()){
$sidebar = ‘Blog’;
}

if(!dynamic_sidebar($sidebar)){
echo “Could not find sidebar”;
}

?>
</div>

When I change the permalinks to prettypermalinks it breaks the sidebar and get this error “Could not find sidebar”

When I change the permalinks back to default it works again.

Does anyone have any idea of the issue? Thanks