A message was sent to a channel
{
"type": "message",
"subtype": "channel_leave",
"ts": "1358877455.000010",
"user": "U2147483828",
"text": "<@U2147483828|cal> has left the channel"
}
A channel_leave message is sent when a member of a channel leaves that
channel.
If you prefer a more atomic event, use member_left_channel instead. Consult the changelog for further guidance.
When an event occurs, we will send an HTTP POST request to your Request URL. The outer payload is uniform across all Events API methods, and contains fields like team_id and event. Learn more