Universal Native App with Payment Integration

I'm looking for a seasoned mobile app developer to create a cross-platform application for iOS, Android, Windows, and web browsers. This app will feature about 8-9 screens and needs to incorporate Google Pay as the primary payment gateway. Key deliverables involve: • Crafting a user-friendly app UI with seamless navigation on all screens • Implementing Google Pay or any other payment gateway into the application for secure and fast transactions • Developing a versatile code base, allowing for my personal management and adaptation Expected Experience: • Proficiency in developing native mobile applications across various platforms • Proven experience in incorporating payment gateways, in this case - Google Pay • Understanding of structured, well-documented, and reusable code I anticipate making occasional content updates. You will handover the completed code base at the project's conclusion. Moreover, you are required to guide me with the set up on my local machine, thereby empowering me to make minor changes, such as modifications to the app color or logo, independently.