I can't access mattermost via url

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For troubleshooting questions, please post in the following format:

Issue in one concise sentence.
Mattermost container is up and running in docker. But I can’t connect using the android app nor server URL.

Steps to reproduce
How can we reproduce the issue (what version are you using?
Mattermost container is running with a healthy status in portainer.

Expected behavior
Describe your issue in detail
I can’t connect using the URL or serverIP:port

Observed behavior
What did you see happen? Please include relevant error messages and/or screenshots.

“Failed to ping db” strongly suggests that Mattermost doesn’t have the correct info to access the database. What does DataSource in config.json look like? Can you use the info there (username, password, hostname) with psql to connect?