Has the class started yet? Class times are shown in your local time, and they become joinable 10 minutes before the class begins. If you don't see a "Join Class" button, the class session has not started yet.

Is the class full? Classes have a maximum student count, though the limit is quite high, so this might be surprising

Are you super late? Classrooms are locked automatically to prevent disruptions. Be sure to be on time!

Are you using Google Chrome or Mozilla Firefox? Classes do not fully support other desktop browsers at this time.