@vinhphat89 in my case, normally i will get the payload like below when i use slack events adapter instead of RASA.
message output: {‘type’: ‘message’, ‘ts’: ‘1545818978.001400’, ‘client_msg_id’: ‘43fb4827-fddd-4dc1-985a-eef3b3b4b1ad’, ‘text’: ‘hi’, ‘channel_type’: ‘im’, ‘channel’: ‘DAT7U3PST’, ‘user’: ‘W94SC8XU7’, ‘event_ts’: ‘1545818978.001400’, ‘team’: ‘T02N7570P’}
In Rasa, sender_id just provides “user” details. Btw i created a new topic on this Find Slack Channel ID.
Thank you very much for your insights 