Cross-Platform Grocery Delivery App

I'm looking for an experienced mobile app developer to create a grocery delivery app for both iOS and Android platforms. The app must include:

- User Authentication: Secure login and registration.
- Real-time Order Tracking: Live updates on order status.
- In-app Payments: Seamless payment processing.

Inventory management for stores is optional.

Ideal skills and experience:
- Proven experience in developing cross-platform mobile apps.
- Strong knowledge of secure authentication methods.
- Experience with real-time data processing and payment gateways.
- Familiarity with inventory management systems is a plus but not required.

Please provide examples of similar work done.