Kotlin & Flutter Feature Enhancement

I need a skilled Kotlin and Flutter developer to add a new feature to our existing mobile application codebase for both Android and iOS platforms. The project needs to be completed within 7 days.

Ideal Skills and Experience:
- Proficiency in Kotlin for Android development.
- Strong experience with Flutter for cross-platform mobile development.
- Familiarity with both Android and iOS development environments.
- Ability to understand and work with existing codebases.
- Should have experience in adding features like user authentication, payment integration, or push notifications.

Please provide examples of similar work done, and ensure you can meet the 7-day deadline.