Productivity App Functional Enhancements

I'm looking for a professional who can customize the functional features of my productivity app. The specific features to be modified are yet to be determined (TBD), but they might include aspects such as user authentication, the payment system, or push notifications.

Ideal Skills:
- Proficiency in app development and customization
- Experience with productivity app development
- Understanding of user authentication systems, payment integrations, and push notification setups
- Strong problem-solving skills to identify and implement necessary enhancements

Experience:
- Prior work on functional customization of apps, particularly productivity apps
- Demonstrable history of improving app performance and user experience
- Portfolio showcasing successful app projects and their impact on productivity

Please provide examples of previous similar projects when bidding.