Hi, Guilherme,
Sorry for such a late reply.
Actually the plugin should work as you’ve described out of the box. The plugin searches for available free shipping methods automatically, so if there are no methods in the current shipping zone (i.e. for current ZIP code), then no message should be displayed. Are you seeing messages for the wrong zones? If that is the case – maybe you have set the “Manual min amount” option in “Advanced Options” (this would explain the problem)? If this is not helping – maybe I could log in to your site to check what’s going on (my email is [email protected])? Please let me know if sharing an account is not an option and I will continue solving it remotely.