Car Wash Slot Booking App

My car-washing center needs a clean, user-friendly mobile app that lets customers choose an available date and time, then lock in their wash slot. I want the same experience on both iOS and Android, so a shared code-base approach such as Flutter, React Native, or another cross-platform framework is welcome as long as performance feels native.

Booking logic
• Customers must be able to make either a one-off appointment or set up a recurring slot (for example, every Friday at 10 a.m.).
• Once a slot is confirmed, the user receives an automatic SMS confirmation that includes the appointment details and a cancellation link.
• The system should block double-booking and clearly show which times are already taken.

Admin view
I need an internal screen or lightweight web dashboard where my staff can:
– Add, edit, or cancel appointments manually
– Set working hours and holiday closures
– View daily, weekly, and monthly calendars at a glance

Data & integrations
The SMS confirmations can run through Twilio or another reliable gateway; whichever you prefer, just note any extra fees in your proposal. Please plan for secure user data storage and a simple login system—email + OTP or a quick social sign-in is fine.

Acceptance criteria
1. Test builds run smoothly on recent iOS and Android devices.
2. Single and recurring bookings work without conflicts.
3. SMS confirmation reaches a real phone during demo.
4. Admin dashboard updates reflect instantly in the customer app.

Source code, build instructions, and any third-party license details must be handed over at project completion. Feel free to suggest UI improvements or additional quality-of-life features if they fit naturally into the workflow.