How do I set bbpress role?

I’m trying to create a bbpress role. Under ‘change capabilities for user’ there is Primary Role, bbpress role and Other role. Where do I add the bbpress role? I would have thought that adding ‘participate’ as a capability would automatically allow them to use the forum but still cannot select a forum role for them. If I select either participate or one of my custom forum roles, it will not save it. It defaults back to ‘no role for these forums’.