Slack App: How do I make it work?

Hi!

I wanted to try the Slack integration, but Slack tells me – even after I successfully authorized Homey in Slack and then selected a workspace – that /flow is not a valid command.

Any ideas what to do?
Did anyone of you folks made it work?

I also can’t see Homey or @Homey2 as a user which I could add to a channel.

Best
Martin