Adding links to gallery items

HI there I’ve followed the following yet nothing is working:

Both the WP Gallery Custom Links plug-in is installed.

Following code is added to the bottom the functions.php file, residing in the enfold-child folder:

add_filter(‘avf_avia_builder_gallery_image_link’, ‘avia_change_gallery_thumbnail_link’, 10, 4);
function avia_change_gallery_thumbnail_link($link, $attachment, $atts, $meta)
{
$custom_url = get_post_meta($attachment->ID, ‘_gallery_link_url’, true);
if(!empty($custom_url))
{
$link[0] = $custom_url;
$link[‘custom_link_class’] = ‘aviaopeninbrowser’;
}
return $link;
}

I’ve added the appropriate links to each of the images (red & grey in tiles) – yet they still trigger the lightboxes. Please assist.