Slack and docker-compose - error

I have been having troubles connecting to Slack using Rasa X and docker-compose

RASA_X_VERSION=0.33.1
RASA_VERSION=2.0.2
Python 3.6

I have done all the configurations as in the documentation but unfortunately I’m not able to send and receive messages successfully.

I have already implemented my bot to use Google Chat, Microsoft Teams, Telegram, socketio and Facebook Messenger, so I know that my webhook is working. However, Slack won’t seem to work.

Here is the log from the running container rasa_nginx_1:

3.85.169.219 - - [01/Feb/2021:17:45:06 +0000] "POST /webhooks/slack/webhook HTTP/1.1" 500 250 "-" "Slackbot 1.0 (+https://api.slack.com/robots)"

Here is the error message from rasa_rasa-production_1:

    [2021-02-01 17:45:06 +0000] [1] [ERROR] Exception occurred while handling uri: 'http://<dns>/webhooks/slack/webhook'
Traceback (most recent call last):
  File "/opt/venv/lib/python3.7/site-packages/sanic/app.py", line 973, in handle_request
    response = await response
  File "/opt/venv/lib/python3.7/site-packages/rasa/core/channels/slack.py", line 422, in webhook
    user_message, metadata["users"]
  File "/opt/venv/lib/python3.7/site-packages/rasa/core/channels/slack.py", line 230, in _sanitize_user_message
    for uid_to_remove in uids_to_remove:
TypeError: 'NoneType' object is not iterable
[2021-02-01 17:45:06 +0000] [1] [ERROR] Exception occurred while handling uri: 'http://<dns>/webhooks/slack/webhook'
Traceback (most recent call last):
  File "/opt/venv/lib/python3.7/site-packages/sanic/app.py", line 973, in handle_request
    response = await response
  File "/opt/venv/lib/python3.7/site-packages/rasa/core/channels/slack.py", line 422, in webhook
    user_message, metadata["users"]
  File "/opt/venv/lib/python3.7/site-packages/rasa/core/channels/slack.py", line 230, in _sanitize_user_message
    for uid_to_remove in uids_to_remove:
TypeError: 'NoneType' object is not iterable
[2021-02-01 17:46:07 +0000] [1] [ERROR] Exception occurred while handling uri: 'http://<dns>/webhooks/slack/webhook'
Traceback (most recent call last):
  File "/opt/venv/lib/python3.7/site-packages/sanic/app.py", line 973, in handle_request
    response = await response
  File "/opt/venv/lib/python3.7/site-packages/rasa/core/channels/slack.py", line 422, in webhook
    user_message, metadata["users"]
  File "/opt/venv/lib/python3.7/site-packages/rasa/core/channels/slack.py", line 230, in _sanitize_user_message
    for uid_to_remove in uids_to_remove:
TypeError: 'NoneType' object is not iterable
[2021-02-01 17:51:07 +0000] [1] [ERROR] Exception occurred while handling uri: 'http://<dns>/webhooks/slack/webhook'
Traceback (most recent call last):
  File "/opt/venv/lib/python3.7/site-packages/sanic/app.py", line 973, in handle_request
    response = await response
  File "/opt/venv/lib/python3.7/site-packages/rasa/core/channels/slack.py", line 422, in webhook
    user_message, metadata["users"]
  File "/opt/venv/lib/python3.7/site-packages/rasa/core/channels/slack.py", line 230, in _sanitize_user_message
    for uid_to_remove in uids_to_remove:
TypeError: 'NoneType' object is not iterable

I have replaced my dns with <dns>

Here is the file credentials.yml:

rest:
# you don't need to provide anything here - this channel doesn't
# require any credentials

rasa:
  url: ${RASA_X_HOST}/api

telegram:
  access_token: "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"
  verify: "xxxxxxxxxxxxx"
  webhook_url: "https://<dns>/webhooks/telegram/webhook"

hangouts:

facebook:
  verify: "xxxxxxxxxxxxx"
  secret: "xxxxxxxxxxxxxxxxxxxxxxx"
  page-access-token: "xxxxxxxxxxxxxxxxxxxxxxxxx"

botframework:
  app_id: "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"
  app_password: "xxxxxxxxxxxxxxxxxxxxxxxxxx"

slack:
  slack_token: "xoxb-xxxxxxxxxxxxxxxxxxxxxxxxxxx"
  slack_channel: "C01KK9E6VAP"
  slack_signing_secret: "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"

socketio:
  user_message_evt: user_uttered
  bot_message_evt: bot_uttered
  session_persistence: true/false

Any tips to fix this?

Best regards, Robyn