OTP Android Service Booking

I need an Android e-commerce application that focuses solely on service bookings rather than physical product sales. The app will open with a simple mobile-number sign-in, verified by OTP (Firebase Phone Auth or any comparable, secure method you prefer).

Core flow
• Users browse three main categories—Home Services (plumbing, cleaning, etc.), Personal Services (haircuts, fitness training, etc.), and Professional Services (consulting, legal advice, etc.).
• Each category contains individual service listings with images, price, short description and an “Add to Booking” button.
• During checkout the only field I want to capture from the customer, aside from the usual contact data already tied to the OTP login, is a free-text Special Instructions box. The design must keep it flexible so future additions like service-location or preferred-time pickers can be plugged in with minimal refactor.

Admin side
I should be able to add, edit or disable categories and listings without touching code—Firebase Firestore, Supabase, or a lightweight custom backend are all fine so long as the interface is clear and the data syncs in real time.

Deliverables
1. Production-ready Android APK and full source (Kotlin or Flutter preferred; Java acceptable).
2. Lightweight admin panel or JSON-driven solution for category/listing management.
3. Clean build/run documentation so I can recompile locally.
4. Brief hand-off session to confirm OTP workflow, category creation and the Special Instructions capture work exactly as described.