I’m also getting this error! No success in a private or public channel, both of which have the bot added.
Did you ever figure this out?
For what it’s worth, my Slack instance has 17,000+ users, so I am wondering if something is going wrong with the users.list endpoint? I am able to successfully return a very long users.list response via Slack’s API tester, using the same token provided in Discours settings. users.list method | Slack
One theory on what might be going wrong: it looks like Discourse is paginating 200 users at a time, which would require 85+ API calls.
Users.list is a Tier 2 rate limited endpoint:
Web API Tier 2
20+ per minute
Most methods allow at least 20 requests per minute, while allowing for occasional bursts of more requests.
Is it possible that this is a rate limit issue?
I also can’t seem to access any more detailed log info on this, on my discourse hosted instance. But happy to help debug if useful!