What external systems must the app integrate with? (payment gateway, SMS, email, CRM/ERP, website, external APIs). Are existing APIs ready, or do they still need to be designed and implemented? Who owns them? What data will the app read/write? Any complex workflows like sync, background jobs, real‑time updates (WebSockets, push)?​ Do you need offline mode or local caching? If yes, what data must be available offline?