You’re waiting in the lobby: Some organizers might place attendees in a lobby before admitting them into the meeting. Wait for someone to admit you, or reach out to the organizer directly to be let in.
Your internet browser isn’t supported: Teams doesn’t currently support Safari for Mac. If you’re joining a Teams meeting from the web, try joining from Microsoft Edge, Google Chrome, or other supported browsers.
Your internet connectivity is low: If your internet connection is low, you may not be able to join a Teams meeting right away. Try waiting for your connection to improve, joining from your supported mobile device, or reaching out to your internet provider.
Security policies for the meeting are preventing you from joining: If a meeting organizer enables end-to-end encryption for a meeting, you might have limited access to join. Try reaching out to the organizer to be let in.