This FEP has the same problem as FEP-044f, FEP-7aa9 and other similar proposals: misused activity names. Accept and Reject belong to the "Follow" flow, and the proposed activities are indistinguishable from them. Also, Invite conflicts with prior usage in FEP-bebd: Follow Invites.
Consider changing the names:
- Invite -> InviteAttendee
- Accept -> AcceptInviteAttendee
- Reject -> RejectInviteAttendee
- Join -> JoinEvent
- etc