Android App for Business Transactions

I'm looking to develop an Android app for my business. This app should enable customers to make payments, download receipts and withdraw funds from their wallet.

Key Features:
- Payment processing
- Receipt downloads
- Wallet withdrawal functionality

I have a basic idea for the app but will need your expertise in creating a detailed design.

The only payment method I want integrated into the app for now is PayPal.

Ideal Skills:
- Android App Development
- UX/UI Design
- Payment Integration
- Java/Kotlin
- Experience with PayPal API