KOKADWARAkshay/PaymentGateway ? reverse-engineered prompt

Build me a simple Android app in Java for an all in one UPI payment gateway.

I want a clean app that lets a user enter payment details, choose a UPI app if needed, and make a payment flow that feels easy and straightforward. Make it look polished, work smoothly, and handle success, failure, and cancelled payments with clear messages so the user always knows what happened.

If this project needs Firebase or any current payment related setup, wire it in the way that makes sense here and use the included config files. Keep the code organized and easy to follow, and make the main screen focused on starting a payment quickly. If you need to check current docs online for the best way to do the integration, go ahead and do that. Also add a basic success screen or confirmation view after a payment goes through.