If Chrome is showing a message that 'This site can't be reached' or ERR_CONNECTION_REFUSED then there's a few things to check in your firewall and web filters.
1. You'll need to ensure your devices can access *.bookcreator.com and add it to any whitelists.
2. Book Creator is hosted by Google and they use the same IP addresses for many hosted websites. If your filters are performing a reverse DNS lookup check this may need to be disabled, as the IP addresses for app.bookcreator.com won't reverse back to bookcreator.com