Twilio integration not working

I am having trouble connecting Rasa with Twilio. I’ve followed Rasa’s docs, adding the credentials to credentials.yml, but when I send a message to the Twilio number, I get an Error 11200: HTTP retrieval failure, and no reply is received. I’m at a loss on how to debug this — I know it’s not a problem with my code since my bot works when tested locally. Here are the contents of the relevant files:

credentials.yml:

twilio:
  account_sid: (not shown)
  auth_token: (not shown)
  twilio_number: (not shown)

endpoints.yml:

action_endpoint:
   url: "http://localhost:5055/webhook"

docker-compose.yml:

version: '2.4'

services:

  rasa:
    image: rasa/rasa:2.7.0-full
    ports:
      - 5005:5005
    command: run --endpoints endpoints.yml --credentials credentials.yml --connector twilio --enable-api --debug
    volumes:
      - ./models:/app/models    
      - ./credentials.yml:/app/credentials.yml
      - ./endpoints.yml:/app/endpoints.yml

  app:
    image: rasa/rasa-sdk:2.7.0
    ports:
    - "5055:5055"
    volumes:
    - ./actions:/app/actions
    expose:
    - "5055"

  duckling:
    image: rasa/duckling:latest
    ports:
    - "8000:8000"

@alexyuwen What is the version twillo?

@nik202 The Twilio version is 6.50.1