Verify Paystack Payments in Flutter

Your Flutter app calls this endpoint after checkout. The backend calls Paystack:

// Node.js/Express backend
app.get('/api/pay/verify', async (req, res) => {
  var reference = req.query.reference;
  if (!reference) return res.status(400).json({ error: 'Reference required' });

  var response = await fetch(
    'https://api.paystack.co/transaction/verify/' + encodeURIComponent(reference),
    {
      headers: { Authorization: 'Bearer ' + process.env.PAYSTACK_SECRET_KEY }
    }
  );

  var data = await response.json();

  if (!data.status || data.data.status !== 'success') {
    return res.status(400).json({
      verified: false,
      status: data.data?.status || 'error',
      message: data.data?.gateway_response || 'Payment not verified'
    });
  }

  res.json({
    verified: true,
    amount: data.data.amount / 100,
    currency: data.data.currency,
    reference: data.data.reference,
    customer_email: data.data.customer.email
  });
});

// lib/services/payment_service.dart
import 'package:http/http.dart' as http;
import 'dart:convert';

class PaymentResult {
  final bool verified;
  final double? amount;
  final String? currency;
  final String? reference;
  final String? errorMessage;

  const PaymentResult({
    required this.verified,
    this.amount,
    this.currency,
    this.reference,
    this.errorMessage,
  });
}

class PaymentService {
  static const String _baseUrl = 'https://your-backend.com';

  static Future<PaymentResult> verify(String reference) async {
    try {
      var response = await http.get(
        Uri.parse('$_baseUrl/api/pay/verify?reference=$reference'),
        headers: {'Content-Type': 'application/json'},
      ).timeout(const Duration(seconds: 15));

      var data = jsonDecode(response.body);

      if (response.statusCode == 200 && data['verified'] == true) {
        return PaymentResult(
          verified: true,
          amount: (data['amount'] as num).toDouble(),
          currency: data['currency'],
          reference: data['reference'],
        );
      } else {
        return PaymentResult(
          verified: false,
          errorMessage: data['message'] ?? 'Verification failed',
        );
      }
    } catch (e) {
      return PaymentResult(
        verified: false,
        errorMessage: 'Network error: ${e.toString()}',
      );
    }
  }
}

// lib/payment_result_screen.dart
import 'package:flutter/material.dart';
import 'services/payment_service.dart';

class PaymentResultScreen extends StatefulWidget {
  final String reference;

  const PaymentResultScreen({super.key, required this.reference});

  @override
  State<PaymentResultScreen> createState() => _PaymentResultScreenState();
}

class _PaymentResultScreenState extends State<PaymentResultScreen> {
  late Future<PaymentResult> _verifyFuture;

  @override
  void initState() {
    super.initState();
    _verifyFuture = PaymentService.verify(widget.reference);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: FutureBuilder<PaymentResult>(
        future: _verifyFuture,
        builder: (context, snapshot) {
          if (snapshot.connectionState == ConnectionState.waiting) {
            return const Center(
              child: Column(
                mainAxisAlignment: MainAxisAlignment.center,
                children: [
                  CircularProgressIndicator(),
                  SizedBox(height: 16),
                  Text('Verifying payment...'),
                ],
              ),
            );
          }

          if (!snapshot.hasData || !snapshot.data!.verified) {
            return Center(
              child: Column(
                mainAxisAlignment: MainAxisAlignment.center,
                children: [
                  const Icon(Icons.error_outline, size: 64, color: Colors.red),
                  const SizedBox(height: 16),
                  Text(snapshot.data?.errorMessage ?? 'Payment failed'),
                  TextButton(
                    onPressed: () => Navigator.of(context).pop(),
                    child: const Text('Try Again'),
                  ),
                ],
              ),
            );
          }

          var result = snapshot.data!;
          return Center(
            child: Column(
              mainAxisAlignment: MainAxisAlignment.center,
              children: [
                const Icon(Icons.check_circle, size: 64, color: Colors.green),
                const SizedBox(height: 16),
                const Text('Payment Successful', style: TextStyle(fontSize: 24)),
                const SizedBox(height: 8),
                Text('${result.currency} ${result.amount?.toStringAsFixed(2)}'),
                const SizedBox(height: 8),
                Text('Ref: ${result.reference}', style: const TextStyle(color: Colors.grey)),
              ],
            ),
          );
        },
      ),
    );
  }
}

This guide is part of the Paystack integration guides by language and framework series.

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