Assuming that both FooBB and BarBB are identical, then there should be no reason that federation does not work. In reality of course, there are lots of reasons that can get in the way of things
Are you able to reset the category synchronization settings on both categories so that it's blank?
You should be able to have FooBB add
[email protected], and vice versa, using their handles. That's the tested approach.
It might say pending at first but NodeBB should automatically confirm the follow and "pending" should go away. If it doesn't, then it's a sign that something happened along the way that interrupted the follow-accept handshake.
For AP logging, run NodeBB in development mode: NODE_ENV=development or ./nodebb dev.