Featured image doesn’t work | WordPress.org

I reviewed the source code of your theme and, unfortunately, they’re not using the filters our plugin relies on. Contact the theme author and ask them to wrap the $feat_image in a custom filter. Something like this:

$feat_image = apply_filters( 'cleanblog_featured_image', $feat_image, $post->ID );

and then you’ll be able to add a tiny snippet in your site that checks if the provided post ID has an external featured image and, if it does, use it:

add_filter(
  'cleanblog_featured_image',
  function( $url, $post_id ) {
    $aux = Nelio_Content_External_Featured_Image_Helper::instance();
    $efi = $aux->get_external_featured_image( $post_id );
    return empty( $efi ) ? $url : $efi;
  },
  10,
  2
);