Where is the nerve center of virtual nonprofit?

When the Free Speech Foundation, doing business as America’s Frontline Doctors (“AFLDS”), and its Chairman of the Board filed suit in federal court alleging that its founder was going rogue and interfering with its activities, they were required to prove that the “citizenship” of all of the defendants was different from the citizenship of all of the plaintiffs in order to obtain “diversity jurisdiction” to have a federal court to hear the case.