"Nothing happened" is three different states wearing one face

Some requests are not answered by the system you sent them to. They are answered by a person — another participant approving a join, a peer accepting a transfer — and that person may take a minute, or never look. If the only states you model are "not in" and "in", then a mistyped code, a peer who declined, a peer who is asleep, and a message that never left the device all render identically: the button was pressed and the screen did not change.

One nullable field fixes all four: