If you are in a friend only instance belonging to someone else, and receive a request invite, you get a notification that looks like: "[Person] would like to join. You can ask [instance owner] to invite them."

Clicking accept on this notification does nothing. The text, however, suggests that hitting accept would forward the invite request on to the instance owner, who could then choose to accept or decline the invite.

Notably, as it stands, in a friends only instance, the instance owner actually _can't_ invite the person trying to get in, as they are (evidently) not yet friends.