Usually a Room won't let you in because it is full, because the owner limited who can enter, or because you were removed or blocked. The message you see tells you which one. Find it below.
"Room Full"
Every Room has a visitor limit set by its owner. When it's full, you can try again or tap Join New Room to go somewhere else. You may also be able to join as a spectator and watch until a spot opens, if the owner allows spectating; spectators can't chat until they join the room. Try again a little later, or ask the owner to raise the limit.
"You may not enter this room"
The owner has limited who can enter, for example to friends, followers, or their Crew, and you don't match. This message also appears if the room owner has blocked you. Only the owner can change either.
"You have been banned from this room"
The owner or a room moderator removed you. Room bans can be temporary or permanent, they only apply to that room or World, and they are managed by that room's owner and moderators. See Why was I kicked, muted, or banned from a Room or World?
The room asks me to verify my age
The room is marked 18+, and only players who have verified they are 18 or older can enter. See 18+ verified-only spaces.
The room asks me to update the app
The room uses features your app version doesn't support yet. Update Highrise from your app store and try again.
"World is Out of Date" or "New Version Available"
World is Out of Date: the World no longer works with the current app, and its creator has been told to update it. Try again after the creator publishes an update.
New Version Available with Join Anyway: a newer version of the World exists. You can join now, but updating the app gives you the latest version.
"Room Unavailable" or "World Unavailable"
The room or World was deleted, or the link is out of date. Search for the room again in the Directory.
Why can't I get into an event room?
Many events run in their own World. Each event room has its own player limit, and when the event World is closed or the event ends, its rooms close too. If you can't get into an event room, try another one from the event's entry point, or create your own if the event allows it. For event Worlds that won't load at all, see Why can't I get into an event world?
Why am I stuck loading or kicked out right after joining?
Check your connection, then fully close and reopen Highrise.
Update to the latest version.
Try a different room. If every room fails, it's a connection or app problem rather than a room problem.
When should I contact Support?
Contact Support through How do I contact support? if you can't join any room at all, or you are locked out of your own room. Include the room name or link, the exact message you see, your device and app version, and the time it happened.