Redirect sub-page URLs to parent without changing URL

Question

I am having an issue with redirect rules for a single-page app that is on a sub-page of a Wordpress site. I have followed this set of instructions pretty directly and am still having issues: Redirect sub-pages to parent without changing URL

The subpages are custom post types for business locations. When someone visits http://business.com/hollywood-ca/contact it should pull up http://business.com/hollywood-ca/ but the url needs to remain the same (The contact portion of the URL is part of a single-page Vue.js app on each location page, so it needs to stick around). Here is my code:

//This function hooks in on post save
function add_location_deep_links( $post_id, $post, $update ) {

    $post_type = get_post_type($post_id);

    if ( "location" != $post_type ) return; // If this isn't a 'location' post, don't update it.

    $slug = $post->post_name; //hollywood-ca

    add_rewrite_rule(
        "^{$slug}/[A-Za-z]",  //regex prevents trying to redirect the /hollywood-ca/ page
        "index.php?page_id={$post_id}", //redirect to post
        'top' // take precedence over other redirects
    );

    flush_rewrite_rules();
}

The problem is when I visit http://business.com/hollywood-ca/contact the page redirects to http://business.com/hollywood-ca/ which prevents my single-page app from navigating to the contact tab.

If it helps, I have also written a couple of functions that change my URLs from business.com/location/hollywood-ca to the cleaner business.com/hollywood-ca. I have tested these issues without those functions and am still having issues, so I don't think they are related.

Answer 1

Milo's comment got me there:

add_rewrite_rule(
    "^{$slug}/",  
    "index.php?location={$slug}", //changed query var to location
    'top'
);