WalletConnect POS SDK - Flutter Installation

final posClient = PosClient(
 projectId: projectId,
 deviceId: 'unique_device_id',
 metadata: metadata,
);

final metadata = Metadata(
  merchantName: 'Name of Merchant', // This will appear in the connect screen
  description: 'Short Description',
  url: 'url_web_page',
  logoIcon: 'https://example.com/icon.png',
);

final tokens = [
  PosToken(
    network: PosNetwork(name: 'Ethereum', chainId: 'eip155:1'),
    symbol: 'USDC',
    standard: 'erc20', // Token standard (erc20 for EVM tokens)
    address: '0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48', // USDC contract address on Ethereum
  ),
  PosToken(
    network: PosNetwork(name: 'Polygon', chainId: 'eip155:137'),
    symbol: 'USDC',
    standard: 'erc20',
    address: '0x2791Bca1f2de4661ED88A30C99A7a9449Aa84174', // USDC contract address on Polygon
  ),
];

// Set the tokens (this automatically configures supported networks)
posClient.setTokens(tokens: tokens);

await posClient.init(); // throws on error

// Create a payment intent
final paymentIntent = PaymentIntent(
  token: PosToken(
    network: PosNetwork(name: 'Ethereum', chainId: 'eip155:1'),
    symbol: 'USDC',
    standard: 'erc20',
    address: '0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48',
  ),
  amount: '25.50', // Amount as string (e.g., "12.5")
  recipient: '0xYourMerchantAddress', // Your wallet address
);

// Create the payment intent
await posClient.createPaymentIntent(paymentIntents: [paymentIntent]);

@freezed
sealed class PaymentIntent with _$PaymentIntent {
  const factory PaymentIntent({
    required PosToken token,   // PosToken value (see below)
    required String amount,    // double as String, i.e. `12.5`
    required String recipient, // recipient address, 0x..... for EVM
  }) = _PaymentIntent;
}

@freezed
sealed class PosToken with _$PosToken {
  const factory PosToken({
    required PosNetwork network, // PosNetwork value (see below)
    required String symbol, // i.e. USDC, USDT
    required String standard, // `erc20` for EVM, `token` for Solana, `trc20` for Tron
    required String address, // Contract address on the given chain
  }) = _PosToken;
}

sealed class PosNetwork with _$PosNetwork {
  const factory PosNetwork({
    required String name, // i.e. `Ethereum`
    required String chainId // CAIP-2 chainId. i.e `eip155:1`
    }) = _PosNetwork;
}

// events.dart
abstract class PosEvent extends EventArgs {}

class InitializedEvent extends PosEvent {}

// connection events

class QrReadyEvent extends PosEvent {
  final Uri uri;
  QrReadyEvent(this.uri);
}

class ConnectedEvent extends PosEvent {}

// payment request events
class PaymentRequestedEvent extends PosEvent {}

// payments checking events
class PaymentBroadcastedEvent extends PosEvent {}
class PaymentSuccessfulEvent extends PosEvent {
  final String txHash;
  PaymentSuccessfulEvent(this.txHash);
}

class DisconnectedEvent extends PosEvent {}

// events.dart
abstract class PosErrorEvent extends PosEvent {}

// connection events
class ConnectRejectedEvent extends PosErrorEvent {}
class ConnectFailedEvent extends PosErrorEvent {
  final String message;
  ConnectFailedEvent(this.message);
}

// payment request events
class PaymentRequestRejectedEvent extends PosErrorEvent {}
class PaymentRequestFailedEvent extends PosErrorEvent {
  final String message;
  final PosApiError apiError;
  final String shortMessage;
  PaymentRequestFailedEvent(
    this.message, [
    this.apiError = PosApiError.unknown,
    this.shortMessage = '',
  ]);
}

// payments checking events
class PaymentFailedEvent extends PosErrorEvent {
  final String message;
  final PosApiError apiError;
  final String shortMessage;
  PaymentFailedEvent(
    this.message, [
    this.apiError = PosApiError.unknown,
    this.shortMessage = '',
  ]);
}

enum PosApiError {
  invalidAsset,
  invalidRecipient,
  invalidSender,
  invalidAmount,
  invalidAddress,
  invalidWalletResponse,
  invalidTransactionId,
  failedToEstimateGas,
  invalidProviderUrl,
  rpcError,
  internal,
  invalidFormat,
  invalidChainId,
  insufficientFundsForTransfer,
  transferAmountExceedsBalance,
  broadcastFailed,
  unknown,
}

posClient.onPosEvent.subscribe((event) {
  if (event is QrReadyEvent) {
    // When payment intent is created and connection with the relay is established, this event will contain the pairing URI to create the QR.
    // You can use your own QR Widget but `QrImageView(data: uri)` Widget is available for you to use.
    status = '1. Scan QR code with your wallet';
  } else if (event is ConnectRejectedEvent) {
    // User rejected the wallet connection
    status = '2. User rejected session';
  } else if (event is ConnectFailedEvent) {
    // Connection failed with error message
    status = '2. Connection failed: ${event.message}';
  } else if (event is ConnectedEvent) {
    // Customer connected their wallet upon scanning the QR code with the pairing URI
    status = '2. Connected!';
  } else if (event is PaymentRequestedEvent) {
    // Payment has been sent to the wallet for user approval
    status = '3. Requesting payment...';
  } else if (event is PaymentRequestRejectedEvent) {
    // User rejected the payment request
    status = '3. User rejected payment.';
    final PosApiError apiError = event.apiError;
    final String shortMessage = event.shortMessage;
    final String fullErrorMessage = event.message;
  } else if (event is PaymentFailedEvent) {
    // Payment request failed
    status = '3. Payment request failed.';
  } else if (event is PaymentBroadcastedEvent) {
    // User approved the payment and transaction was broadcasted
    status = '4. Payment broadcasted, waiting confirmation...';
  } else if (event is PaymentFailedEvent) {
    // Payment failed with error message
    status = '4. Payment failed: ${event.message}';
    final PosApiError apiError = event.apiError;
    final String shortMessage = event.shortMessage;
    final String fullErrorMessage = event.message;
  } else if (event is PaymentSuccessfulEvent) {
    // Payment has been confirmed on the blockchain
    status = '4. Payment successful!. Hash: ${event.txHash}';
  } else if (event is DisconnectedEvent) {
    // Session disconnected
    status = '5. Disconnected';
  }
});

// Full reinitialization, clears all state
// Mainly if you want to call init() again
// ✅ recommended option to fully restart the flow, requires setTokens() and init() to be called again
await posClient.restart(reinit: true);

// If for some reason you don't want/need to fully restart the flow don't use `reinit:`
// Abort current payment and restart the flow
await posClient.restart();

flutter pub add pos_client

import 'package:flutter/material.dart';
import 'package:pos_client/pos_client.dart';

class PaymentScreen extends StatefulWidget {
  const PaymentScreen({super.key});

  @override
  State<PaymentScreen> createState() => _PaymentScreenState();
}

class _PaymentScreenState extends State<PaymentScreen> {
  PosEvent? _event;
  String status = '';
  late final IPosClient posClient;
	
	// USDC on Arbitrum
  final supportedToken = PosToken(
    network: PosNetwork(name: 'Arbitrum One', chainId: 'eip155:42161'),
    symbol: 'USDC',
    standard: 'erc20',
    address: '0xaf88d065e77c8cC2239327C5EDb3A432268e5831',
  );

  @override
  void initState() {
    super.initState();
    // [PosClient SDK API] 1. Construct your PosClient instance
    final metadata = Metadata(
      merchantName: 'Merchant Name',
      description: 'Secure Crypto Payment Terminal',
      url: 'https://merchant-url.com',
      logoIcon: 'https://merchant-url.com/icon.png',
    );
    posClient = PosClient(
      projectId: '87....', // TODO set your own project ID
      deviceId: 'device_id',
      metadata: metadata,
    );
    // [PosClient SDK API] 2. call setTokens to construct namespaces with your supported tokens and network
    posClient.setTokens(
      tokens: [
        supportedToken,
      ],
    );

    // [PosClient SDK API] 3. Subscribe to events
    posClient.onPosEvent.subscribe(_onPosEvent);

    // [PosClient SDK API] 4. initialize PosClient SDK. Can be awaited if needed
    posClient.init().then((_) {
      // [PosClient SDK API] 5. create a payment intent with the PaymentIntent. Can be awaited if needed
      posClient.createPaymentIntent(
        paymentIntents: [
          PaymentIntent(
            token: posClient.configuredTokens.first,
            amount: '1.0',
            recipient: '0xD6....', // TODO set your own recipient
          ),
        ],
      );
    });
  }

  void _onPosEvent(PosEvent event) {
    setState(() {
      if (event is QrReadyEvent) {
        status += '1. Scan QR code with your wallet';
      } else if (event is ConnectRejectedEvent) {
        status += '\n2. User rejected session';
      } else if (event is ConnectFailedEvent) {
        status += '\n2. Connection failed: ${event.message}';
      } else if (event is ConnectedEvent) {
        status += '\n2. Connected!';
      } else if (event is PaymentRequestedEvent) {
        status += '\n3. Requesting payment...';
      } else if (event is PaymentRequestRejectedEvent) {
        status += '\n3. User rejected payment.';
      } else if (event is PaymentBroadcastedEvent) {
        status += '\n4. Payment broadcasted, waiting confirmation...';
      } else if (event is PaymentFailedEvent) {
        status += '\n4. Payment failed: ${event.message}';
      } else if (event is PaymentSuccessfulEvent) {
        status += '\n4. Payment successful!. Hash: ${event.txHash}';
      } else if (event is DisconnectedEvent) {
        status += '\n5. Disconnected';
      }
      _event = event;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Crypto Payment')),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            (_event is QrReadyEvent)
                ? QrImageView(
                    data: (_event as QrReadyEvent).uri.toString(),
                    size: 250,
                  )
                : SizedBox.shrink(),
            SizedBox(height: 20),
            Padding(padding: const EdgeInsets.all(8.0), child: Text(status)),
          ],
        ),
      ),
    );
  }
}