For Wordpress sites, chat administrators can control if they want to give access to chat to Guest/Unregistered users also or just the logged-in users.
To do so, please go to App Dashboard
Now go to Settings -> Login. There is an option called Allow Guest Users. Set it to Read & Write. This will enable guest users to access chat and send messages.
To allow only logged-in users to chat and disable Guest Users, set the option Allow Guest Users to Disable.