Cross-Platform E-Commerce App

I am building an Android and iOS e-commerce application focused on selling digital products. The finished apps must feel fast, polished, and intuitive, with a clean, modern interface consistent across both platforms.

Core flow
• New users create an account through phone-number verification (this method is mandatory), then complete a short profile.
• Returning users log in, browse the catalogue, purchase digital items, receive the download or activation instantly, and get notified of updates through in-app and push notifications.
• An admin panel lets me manage users, content, orders, and analytics securely in real time.

Scope of work
1. UI/UX design for mobile and web admin, including dark/light themes.
2. Front-end development (Kotlin/Swift/Flutter/React Native—open to your proven stack) and responsive web admin interface.
3. Back-end with secure database, REST/GraphQL APIs, payment gateway for digital goods, notification service, and GDPR-compliant data handling.
4. Integration testing, unit tests, performance optimisation, and store compliance checks.
5. Deployment to Google Play and the App Store, plus handover of source code and documentation.

Acceptance criteria
• Phone verification works flawlessly in all target regions.
• Purchases of digital items complete end-to-end within 10 seconds.
• Admin actions sync to the apps in real time.
• Both apps pass review and are live in their respective stores.

Please include links to at least three comparable apps you have shipped, along with a rough cost breakdown and realistic timeline so I can align internal milestones before kickoff.