A: chat moderation -- you can delete messages and also block people. "block" is actually a "shadow ban" -- it allows them to keep chatting and from their point of view, it looks like they are posting like normal, but nobody sees anything they post. If you're looking to pre-approve each post, we don't have that.

Certificate of the students -- I'm guessing you're asking to make a list of email addresses who are allowed to join. If so we don't have that. If you're asking about something else, please clarify