Can't accept invitation for organisation to join enterprise

[dkfellows]

I'm in the middle of setting up an organisation that will be within my enterprise, and when I go to the enterprise page I can see that the organisation has been invited, but I can't find how to accept the invitation! The billing settings page (as linked to from the enterprise page) simply has no link or button for me to complete accepting the invitation.

Am I missing something obvious here?