If you have viewers watching from a network that has a firewall service in place, such as a school or a corporation, they may need to whitelist a few domains in order for them to watch your live event.
The domains their network administrator should whitelist are:
cdn.livestream.com
api.new.livestream.com
playback2.akamaized.net/*
playback.akamaized.net/*
livestream-f.akamaihd.net/*
secure-playlist.livestream.com/*
If you are producing a live event, see here for network configuration requirements for streaming to Livestream.