Social meta for blog app

I know this is a topic that is often posted here but I've been through all the posts and tried a variety of methods and still, I can't seem to get this working.

I did note that Drew replied to one thread where he set up his own test and managed to get it working so I can only think that most of us are missing a step somewhere along the line.

The meta templates are exactly the same as per the documentation: https://solutions.grabaperch.com/integrations/facebook-and-twitter-sharing

perch version: 2.8.13

So I have the following setup.

header.php

if (!perch_layout_var('blog', true)) {
    $domain        = 'https://'.$_SERVER["HTTP_HOST"];
    $url           = $domain.$_SERVER["REQUEST_URI"];
    $sitename      = "My site name";
    $twittername   = "@mysitename";
    $sharing_image = '/images/social_tile_fallback_img.jpg';

    PerchSystem::set_var('domain',$domain);
    PerchSystem::set_var('url',$url);
    PerchSystem::set_var('sharing_image',$sharing_image);
    PerchSystem::set_var('twittername',$twittername);
    echo "<!-- this is not the blog -->";
} else {
    echo "<!-- this is the blog -->";
}

perch_page_attributes(array(        
  'template' => 'default.html'    
));

And calling the header in my post.php

# get the post
$post = perch_blog_custom(array(
    'filter' => 'postSlug',
    'match' => 'eq',
    'value' => perch_get('s'),
    'template'   => 'blog/posts.html',
    'skip-template' => true,
    'return-html'   => true,
)); 

# set up the variables
$title       = $post['0']['postTitle'];
$description = strip_tags($post['0']['excerpt']);
if (isset($post[0]['fbimage'])) {
    $fbimage = $post[0]['fbimage'];
} else {
    $fbimage = '';
}
# use the variables in the array value 
perch_page_attributes_extend(array(
    'description'    => $description,
    'og_description' => $description,
    'og_title'       => $title,
    'og_type'        => 'article',
    'sharing_image'  => $fbimage,
    'og_author'      => 'https://www.facebook.com/myfbname',
));

perch_layout('global.header', array(
    'title'           => perch_blog_post_field(perch_get('s'), 'postTitle', true) ,
    'blog' => true,
));

Now when I visit the blog, I can see the comment coming out the indicated the layout variable works, however I see no meta. I've tweaked and played and started from scratch and still nothing. I know there are methods where I could write the meta directly into the page but I am keen to get to the bottom of this issue for future projects as it feels like this is a much cleaner way if I can get it working.

Please let me know if anymore information is required.