Cross-Platform Flutter App Development

I'm seeking an experienced Flutter developer to create a mobile application for both iOS and Android platforms. The app is not a standard social media, e-commerce, or utility app but has unique functionalities.

Key Features:
- User Authentication: Secure login and user management.
- Push Notifications: Real-time updates and alerts.
- User Registration: New user onboarding process.
- Payout Integration: Set up payment processing.
- Order and Reviews Approval Workflow: Manage and approve orders and reviews.

Ideal Skills and Experience:
- Proficiency in Flutter and Dart.
- Experience with integrating payment gateways.
- Strong understanding of mobile app authentication mechanisms.
- Familiarity with push notification services.
- Background in developing approval workflows within apps.

Please provide examples of similar work done and an estimated timeline for completion.