Just found out that free accounts on Heroku are being discontinued: https://blog.heroku.com/next-chapter
I note that the self registration for racket.slack.com is at https://racket-slack.herokuapp.com/
....and it is offline currently.
('m sorry I don't know who manages this so I have posted this on slack and here)
thanks to @soegaard an alternative to the heroku service has been identified.
I've logged an issue that provides details - I unfortunately cannot make the PR as I am not a slack admin and cannot get an invite link
details in the ticket
