You left a channel
Compatibility: RTM Events API
channel_left event is sometimes sent to all connections for a user when that user leaves a channel. It is sometimes withheld.
Clients should respond to this message by closing the channel — this means that when a channel is left from client A, it will automatically be closed in client B.
In addition to this message, all existing members of the channel will receive a
channel_leave message event.
Events API compatibility
Subscribe to this event via the Events API.
Events of this type will be wrapped in metadata when sent via the Events API.