Chat feature inside Lightstream Studio currently available only for Twitch.
You might want to consider using a 3rd Party service that provides a chat overlay for your stream. We have an article on a couple of suggestions that you can consider here. However, this option is only available for the premium tier of Lightstream Studio.
The free tier of Lightstream Studio can only utilize Xsolla Partner Network to create the chat overlay. You can click the banner and it will navigate to the login screen. You can create your chat overlay in the overlay section.
You can also pin your message or other viewers messages to your stream using our native chat platform: