Warning: this comments plugin is operating in compatibility mode

Hello
I put the shortcode with blank in url

<?php echo do_shortcode('[fbcomments][fbcomments url="" width="375" count="off" num="3" countmsg="wonderful comments!"]'); ?>

But i get this message error

Warning: this comments plugin is operating in compatibility mode, but has no posts yet. Consider specifying an explicit ‘href’ as suggested in the comments plugin documentation to take advantage of all plugin features.

https://www.ads-software.com/plugins/facebook-comments-plugin/