DemoPay - Android Payment Demo

A proof-of-concept Android application demonstrating Stripe and Phantom wallet (Solana) payment integrations.

Features

• Stripe Integration: Credit card payments using Stripe SDK with test mode
• Phantom Wallet Integration: Solana Devnet payments via Mobile Wallet Adapter
• Backend API: Node.js server handling payment processing

Prerequisites

1. Android Development:

   • Android Studio
   • Android SDK (API 23+)
   • Java/Kotlin development environment

2. Backend Setup:

   • Node.js (v16 or higher)
   • npm or yarn

3. Accounts & Keys:

   • Stripe Test Account (for publishable and secret keys)
   • Phantom Wallet installed on Android device/emulator

Setup Instructions

1. Backend Setup

cd backend
npm install
cp .env.example .env

Edit .env file:

STRIPE_SECRET_KEY=sk_test_your_actual_stripe_secret_key
SOLANA_PRIVATE_KEY=[your_private_key_array_or_leave_empty_for_auto_generation]
SOLANA_RPC_URL=https://api.devnet.solana.com
PORT=3000

Start the backend server:

npm run dev

The server will run on http://localhost:3000

2. Android Setup

1. Open Android Studio

2. Open the android folder as a project

3. Edit MainActivity.kt and update:

   • STRIPE_PUBLISHABLE_KEY with your actual Stripe publishable key
   • BASE_URL if your backend runs on a different address

4. Sync project with Gradle files

5. Build and run the app

3. Testing

Stripe Payments

• Use test card: 4242 4242 4242 4242
• Any future expiry date
• Any 3-digit CVC

Phantom Wallet

• Install Phantom wallet on your device
• Switch to Devnet/Testnet in Phantom settings
• Connect wallet in the app
• Send test transactions (0.001 SOL)

Project Structure

demopay/
├── android/                 # Android application
│   ├── app/
│   │   ├── src/main/
│   │   │   ├── java/com/demopay/
│   │   │   │   ├── MainActivity.kt
│   │   │   │   └── ApiService.kt
│   │   │   └── res/         # Resources (layouts, strings, etc.)
│   │   └── build.gradle
│   └── build.gradle
├── backend/                 # Node.js server
│   ├── src/
│   │   └── server.js
│   ├── package.json
│   └── .env.example
└── README.md

API Endpoints

Backend Endpoints

• GET /health - Health check and server info
• POST /stripe/create-intent - Create Stripe PaymentIntent
• POST /solana/pay - Send Solana payment
• POST /solana/airdrop - Request SOL airdrop (Devnet only)
• GET /solana/balance/:publicKey - Get wallet balance

Building APK

Debug APK

cd android
./gradlew assembleDebug

APK location: android/app/build/outputs/apk/debug/app-debug.apk

Release APK (for distribution)

cd android
./gradlew assembleRelease

APK location: android/app/build/outputs/apk/release/app-release.apk

Troubleshooting

Common Issues

1. "No wallet found":

   • Install Phantom wallet
   • Ensure it's updated to latest version

2. Network connection failed:

   • Check backend server is running
   • Update BASE_URL in MainActivity.kt
   • For emulator, use http://10.0.2.2:3000
   • For physical device, use your computer's LAN IP

3. Stripe payment fails:

   • Verify Stripe keys are correct
   • Check backend logs for Stripe API errors

4. Solana transaction fails:

   • Ensure wallet is on Devnet
   • Check server has sufficient SOL balance
   • Verify RPC endpoint is accessible

Testing Tips

• Use Android Logcat for debugging: adb logcat | grep DemoPay
• Monitor backend logs for API request details
• Test on both emulator and physical device
• Verify network connectivity between app and backend

Security Notes

⚠️ This is a demo application for testing only:

• Uses Stripe test mode
• Uses Solana Devnet (test network)
• Not production-ready
• Private keys are for development only

Future Enhancements

• Move to Stripe Live mode and Solana Mainnet
• Add transaction signing for arbitrary messages
• Implement proper error handling and retry logic
• Add support for multiple wallet providers
• Improve UI/UX design