The site http://slack.iotatoken.com/ is not working, only the following can be accessed:
Note that https://iotatangle.slack.com is working.
You can access https://slack.iota.org
There is a question here where someone is trying to access the broken url. And @luey replies that the link works (at the time). Might be worth redirecting the old url to the new one if possible, new users might find the old post and get confused