Hi Lis 
So… reminder work very well for it The logic is very similar with my last post contenting actiion.py file
Reminders don’t work with Rest but, i think it will work for slack
channels available
output_channel
string
Enum: "latest" "slack" "callback" "facebook" "rocketchat" "telegram" "twilio" "webexteams" "socketio"
I will build the solution using botfront widget Socket.io and share the project in this thread
Reference: Rasa Reminders are not working in custom UI - #2 by Tobias_Wochinger