Handle Paystack Webhooks in Android with Kotlin

Paystack fires webhooks to your server. Your server then notifies the Android app:

Paystack → Your Backend Server (webhook received + verified)
                     ↓
               Update Database
                     ↓
            FCM Push to Android App
                     ↓
        FirebaseMessagingService handles message
                     ↓
           Update ViewModel / UI

// Node.js backend with Firebase Admin SDK
var crypto = require('crypto');
var admin = require('firebase-admin');

app.post('/api/webhooks/paystack',
  express.raw({ type: 'application/json' }),
  async (req, res) => {
    var sig = req.headers['x-paystack-signature'];
    var hash = crypto
      .createHmac('sha512', process.env.PAYSTACK_SECRET_KEY)
      .update(req.body)
      .digest('hex');

    if (hash !== sig) return res.status(400).send('Invalid signature');
    res.sendStatus(200);

    var event = JSON.parse(req.body.toString());

    if (event.event === 'charge.success') {
      var email = event.data.customer.email;
      var reference = event.data.reference;
      var amount = event.data.amount / 100;

      // Update order in DB
      await db.orders.markAsPaid(reference);

      // Get user's FCM token
      var user = await db.users.findByEmail(email);
      if (user?.androidFcmToken) {
        await admin.messaging().send({
          token: user.androidFcmToken,
          notification: {
            title: 'Payment Received',
            body: 'NGN ' + amount + ' confirmed. Ref: ' + reference
          },
          data: {
            event: 'charge.success',
            reference: reference,
            amount: String(amount)
          }
        });
      }
    }
  }
);

Add Firebase to your Android project, then create a messaging service:

// PaystackMessagingService.kt
import com.google.firebase.messaging.FirebaseMessagingService
import com.google.firebase.messaging.RemoteMessage

class PaystackMessagingService : FirebaseMessagingService() {

    override fun onNewToken(token: String) {
        super.onNewToken(token)
        // Send the new token to your backend
        sendTokenToBackend(token)
    }

    override fun onMessageReceived(message: RemoteMessage) {
        super.onMessageReceived(message)

        val event = message.data["event"]
        val reference = message.data["reference"]
        val amount = message.data["amount"]

        when (event) {
            "charge.success" -> {
                // Send a broadcast that the payment Activity/ViewModel can receive
                val intent = android.content.Intent("com.yourapp.PAYMENT_SUCCESS")
                intent.putExtra("reference", reference)
                intent.putExtra("amount", amount)
                sendBroadcast(intent)

                // Also show a notification
                showNotification("Payment Confirmed", "NGN $amount received")
            }
        }
    }

    private fun showNotification(title: String, body: String) {
        val notificationManager = getSystemService(NOTIFICATION_SERVICE)
            as android.app.NotificationManager
        val channelId = "payment_events"

        if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.O) {
            val channel = android.app.NotificationChannel(
                channelId, "Payment Events",
                android.app.NotificationManager.IMPORTANCE_HIGH
            )
            notificationManager.createNotificationChannel(channel)
        }

        val notification = androidx.core.app.NotificationCompat.Builder(this, channelId)
            .setContentTitle(title)
            .setContentText(body)
            .setSmallIcon(android.R.drawable.ic_dialog_info)
            .setAutoCancel(true)
            .build()

        notificationManager.notify(System.currentTimeMillis().toInt(), notification)
    }

    private fun sendTokenToBackend(token: String) {
        // Use Retrofit to POST the token to your backend
        // Store it so your backend can target this device
    }
}

Register in AndroidManifest.xml:

<service
    android:name=".PaystackMessagingService"
    android:exported="false">
    <intent-filter>
        <action android:name="com.google.firebase.MESSAGING_EVENT" />
    </intent-filter>
</service>

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

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