A separate TeslaFi.com account is required for each vehicle. The logged vehicle for each account can be selected in settings->account->vehicles.
Multiple TeslaFi.com accounts can be linked together from Settings->Account->Vehicle->Create A Fleet Account. Once a fleet account is created a new menu option will appear titled 'Vehicles' from the menu bar where you can easily switch between accounts and manage your fleet account.
Customer support service by UserEcho