Android App Feature Development

I need an experienced Android developer to help with feature development for my app.

Key features to implement include:
- User authentication
- Push notifications
- In-app purchases

Ideal Skills and Experience:
- Proficiency in Android development
- Expertise in Firebase
- Experience with user authentication, push notifications, and in-app purchases
- Strong problem-solving skills
- Good communication skills
Custom solutions

Please provide examples of similar work done.