Seems like after the upgrade to Rasa 2.4.0 dispatcher.utter_message(template=…) does not work properly, Slack SDK emits the warning below, and no message is posted back to Slack:
“UserWarning: The text
argument is missing in the request payload for a chat.postMessage call - It’s a best practice to always provide a text
argument when posting a message. The text
argument is used in places where content cannot be rendered such as: system push notifications, assistive technology such as screen readers, etc.”
All good if downgrading back to Rasa 2.3.4