Comprehensive eCommerce App Development

I'm seeking an experienced developer to help create an eCommerce app for both iOS and Android platforms. The main purpose of the app is to sell products.

Key Features Required:
- Online Payment System integration.

Skills and Experience:
- Demonstrable experience in app development across both platforms.
- Proficiency in payment gateway integration.
- Background in eCommerce is required.
- Proficiency in Swift, Kotlin or relevant languages.
- Familiarity with user-friendly UI design.
Please submit your proposal with related work samples and the strategy you'd adopt for this project.