As of right now, Agora only supports 40 concurrent users within a single world. Once an experience reaches 40 concurrent users, Agora will create multiple instances of the experience. For example, the first 40 people will enter the room "myevent#1". The 41st will enter the room "myevent#2".
If you’re trying to meet up with someone in a specific instance, have them go to the menu while in the experience by pressing Tab. At the top of the menu, they should see their specific room code. Copy that code directly, including the #InstanceNumber after the room code, and paste it within the Join menu. If the instance isn’t completely full - for example if one of the original 40 people in an experience have since left - you’ll be able to join!
The same applies if you are attempting to join a booth room, which has a room code in the format roomCode@boothCode. You also can enter this value as your room code (spaces included!) to directly join a booth. For example, I could directly join coolevent@chillbooth (where the room code is “coolevent” and the booth code is “chillbooth”).