It doesn‘t really matter too much what you do and when. If BusinessApp is supposed to be decoupled from WebApp, but also needs to know details only WebApp is aware of (like urls), then one solution would be to provide these details whenever WebApp calls api of BusinessApp. Something like BusinessApp.start_registration_flow(user, WebApp.business_routes()). That way BusinessApp doesn‘t need to call into WebApp again to get to know those urls.
