I have the exact same problem. The plugin’s settings are set to display the button on posts, but the button doesn’t show up. Looks like the hosted JS isn’t getting injected into the footer? My theme does call wp_footer(). The button also doesn’t show when I manually add the call to pf_show_link() to single.php.
You can access blog posts that are missing the button at silkbush.com/blog/ (click through to view the single post).
I tried installing the plugin on a local dev version of WP and the settings page is hanging when I try to access it, so I can’t troubleshoot very much.