Add external link to Featured image

Picking up where the Featured Image post left off – I’d like to be able to actually link the image to a separate url than the post itself.

I’ve created a custom field for the blog post called url and I have this code in the post_loop_template.php page:

<div class="featured-image">
		<?php $url = get_post_meta($post->ID, 'url', true);?>
<a href="<?php echo $url ?>" title="<?php the_title(); ?>">
					<?php the_post_thumbnail('thumbnail'); ?>
					</a>
	</div>

But the url is not populating. There’s nothing in the a href=””

What am I missing?
Thank you!

https://wordpress.org/plugins/posts-in-page/