I've installed this plugin in a site with a domain like this "word-word.com". When your plugin tries to set the opt_in or opt_out cookie for this site, you extract the tld to get the domain.
The error happens in file /vendor/pf4wp/lib/Pf4wp/Common/Cookies.php below line 75. Your regular expression matches only "word.com" and not "word-word.com". I believe the problem is in your regular expression.
Thanks for your great work anyway!