The docs at https://docs.mattermost.com/install/troubleshooting.html are out of date.
Steps to reproduce
Go to bottom of the page, and see there’s a suggestion to use demo.mattermost.com. I dug around for it, and I’m guessing that it’s a service you no longer provide. If there’s another way to achieve the same result, it would be good to know!
Sorry if this is the wrong place to report this.