Cross-Platform E-commerce App Development

I'm looking for an experienced app developer to create an e-commerce app for both iOS and Android platforms. The app should include a product catalog, a secure payment gateway, and user authentication.

Key Requirements:
- Develop a user-friendly and intuitive product catalog.
- Integrate a secure payment gateway.
- Implement user authentication for a personalized shopping experience.

Ideal Skills and Experience:
- Proven experience in developing e-commerce apps for both iOS and Android.
- Strong knowledge of payment gateway integration.
- Expertise in user authentication mechanisms.
- Familiarity with UI/UX design principles for mobile apps.

Please provide examples of previous work and estimated timelines.