How to Integrate M-Pesa (Daraja API) into Your Mobile App: A Developer’s Guide

const axios = require('axios');

const getAccessToken = async (req, res, next) => {
    const consumerKey = process.env.SAF_CONSUMER_KEY;
    const consumerSecret = process.env.SAF_CONSUMER_SECRET;
    
    // Combine and convert to Base64
    const buffer = Buffer.from(`${consumerKey}:${consumerSecret}`);
    const auth = buffer.toString('base64');

    try {
        const response = await axios.get(
            'https://sandbox.safaricom.co.ke/oauth/v1/generate?grant_type=client_credentials',
            {
                headers: {
                    Authorization: `Basic ${auth}`
                }
            }
        );
        req.token = response.data.access_token;
        next();
    } catch (error) {
        console.error('Error generating M-Pesa access token:', error.response?.data || error.message);
        res.status(500).json({ error: 'Failed to authenticate with payment gateway' });
    }
};

const initiateSTKPush = async (req, res) => {
    const { phone, amount, accountReference, transactionDesc } = req.body;
    const accessToken = req.token;

    const shortCode = process.env.SAF_SHORTCODE; // e.g., 174379 (Sandbox test shortcode)
    const passkey = process.env.SAF_PASSKEY;
    
    // Generate timestamp
    const date = new Date();
    const timestamp = 
        date.getFullYear().toString() +
        String(date.getMonth() + 1).padStart(2, '0') +
        String(date.getDate()).padStart(2, '0') +
        String(date.getHours()).padStart(2, '0') +
        String(date.getMinutes()).padStart(2, '0') +
        String(date.getSeconds()).padStart(2, '0');

    const password = Buffer.from(`${shortCode}${passkey}${timestamp}`).toString('base64');

    // Format phone number to 2547XXXXXXXX
    const formattedPhone = phone.startsWith('0') ? `254${phone.slice(1)}` : phone;

    try {
        const response = await axios.post(
            'https://sandbox.safaricom.co.ke/mpesa/stkpush/v1/processrequest',
            {
                BusinessShortCode: shortCode,
                Password: password,
                Timestamp: timestamp,
                TransactionType: 'CustomerPayBillOnline',
                Amount: amount,
                PartyA: formattedPhone,
                PartyB: shortCode,
                PhoneNumber: formattedPhone,
                CallBackURL: 'https://yourdomain.com/api/v1/mpesa/callback',
                AccountReference: accountReference,
                TransactionDesc: transactionDesc
            },
            {
                headers: {
                    Authorization: `Bearer ${accessToken}`
                }
            }
        );

        res.status(200).json({
            success: true,
            message: 'STK push initiated successfully',
            data: response.data
        });
    } catch (error) {
        console.error('STK Push Error:', error.response?.data || error.message);
        res.status(400).json({
            success: false,
            error: error.response?.data || 'Failed to initiate STK push'
        });
    }
};

{
  "Body": {
    "stkCallback": {
      "MerchantRequestID": "29115-34620561-1",
      "CheckoutRequestID": "ws_CO_191220191020363925",
      "ResultCode": 0,
      "ResultDesc": "The service request is processed successfully.",
      "CallbackMetadata": {
        "Item": [
          { "Name": "Amount", "Value": 100.00 },
          { "Name": "MpesaReceiptNumber", "Value": "NLJ7RT61SV" },
          { "Name": "Balance" },
          { "Name": "TransactionDate", "Value": 20191219102100 },
          { "Name": "PhoneNumber", "Value": 254712345678 }
        ]
      }
    }
  }
}

const handleMpesaCallback = async (req, res) => {
    try {
        const callbackData = req.body.Body.stkCallback;
        const merchantRequestId = callbackData.MerchantRequestID;
        const checkoutRequestId = callbackData.CheckoutRequestID;
        const resultCode = callbackData.ResultCode;
        const resultDesc = callbackData.ResultDesc;

        if (resultCode === 0) {
            // Transaction Successful
            const metadataItems = callbackData.CallbackMetadata.Item;
            const amount = metadataItems.find(item => item.Name === 'Amount').Value;
            const mpesaReceiptNumber = metadataItems.find(item => item.Name === 'MpesaReceiptNumber').Value;
            const phoneNumber = metadataItems.find(item => item.Name === 'PhoneNumber').Value;
            const transactionDate = metadataItems.find(item => item.Name === 'TransactionDate').Value;

            // TODO: Update your database (e.g., mark order as Paid, generate receipt)
            console.log(`Payment successful for Receipt: ${mpesaReceiptNumber}, Amount: ${amount}`);
        } else {
            // Transaction Failed or Cancelled by User
            console.log(`Payment failed: ${resultDesc}`);
            // TODO: Update order status as Cancelled/Failed in database
        }

        // Always acknowledge receipt of callback to Safaricom
        res.status(200).json({ ResultCode: 0, ResultDesc: 'Accepted' });
    } catch (error) {
        console.error('Error handling callback:', error);
        res.status(500).json({ ResultCode: 1, ResultDesc: 'Failed to process callback' });
    }
};

import 'dart:convert';
import 'package:http/http.dart' as http;

Future<void> triggerMpesaPayment(String phone, double amount) async {
  final url = Uri.parse('https://api.yourdomain.com/api/v1/mpesa/stk-push');

  try {
    final response = await http.post(
      url,
      headers: {'Content-Type': 'application/json'},
      body: jsonEncode({
        'phone': phone,
        'amount': amount,
        'accountReference': 'Order #1024',
        'transactionDesc': 'Payment for digital services',
      }),
    );

    if (response.statusCode == 200) {
      // Prompt user to check phone for STK popup
      print('STK Push sent successfully. Check your phone.');
    } else {
      print('Failed to initiate payment.');
    }
  } catch (e) {
    print('Network error: $e');
  }
}