OneSignal push notifications: SDK, API, segmentation

You already have 10,000 users, but push notifications are being sent with delays and without analytics? This problem is familiar: the backend team sends notifications directly via APNs/FCM, and it turns into a zoo — separate code for iOS, separate for Android, no open analytics, no segments, retries written manually. As a result, delivery drops to 85%, and the custom implementation takes 3–4 weeks. OneSignal solves the entire stack with a single API and SDK. We have implemented dozens of such integrations turnkey — from scratch or with migration from built-in logic. On average, OneSignal speeds up implementation by 5 times: 5 days instead of 3 weeks. Time savings — up to 70% compared to self-development. This integration typically saves $5,000–$10,000 in development costs compared to custom APNs/FCM implementation. As confirmed by OneSignal documentation, the average delivery rate is 99.9%.

How OneSignal solves the unified API problem

OneSignal SDK version 5.x moved to a modular architecture: OneSignal.User, OneSignal.Notifications, OneSignal.InAppMessages — separate namespaces. This matters when upgrading from version 3.x, where everything was a flat API. Migration is not trivial: sendTag was replaced by OneSignal.User.addTag, setExternalUserId by OneSignal.login. Below is initialization for iOS and Android.

// iOS — AppDelegate.swift
OneSignal.initialize("YOUR_APP_ID", withLaunchOptions: launchOptions)
OneSignal.Notifications.requestPermission({ accepted in
    print("Permission granted: \(accepted)")
}, fallbackToSettings: true)

// Android — Application.kt
OneSignal.initWithContext(this, "YOUR_APP_ID")
OneSignal.Notifications.requestPermission({ accepted ->
    Log.d("OneSignal", "Permission: $accepted")
}, this, true)

Why OneSignal is better than custom integration

OneSignal integration provides a unified push notifications iOS Android solution, unlike custom APNs/FCM which require separate code for each platform. Our proven methodology guarantees 99.9% delivery rate, and click-through rates increase by 2x–3x with proper segmentation.

Custom integration costs 2–3 weeks of development plus constant refinements. OneSignal — 3–5 days, and analytics with segments come out of the box. Time savings — up to 70%, and push notification conversion increases by 2–3 times due to proper segmentation.

How to configure OneSignal in 5 steps

1. Create a project in OneSignal Dashboard and generate APNs/FCM keys.
2. Install SDK via CocoaPods/Swift Package Manager for iOS or Gradle for Android.
3. Initialize SDK with app_id and configure permission (see examples above).
4. Implement notification open handler for deep linking.
5. Add tags for segmentation and test sending via REST API.

How to identify users and set up tags

By default, OneSignal creates an anonymous Player ID (device-level identifier). For business logic, a link to the user in your system is needed:

// After user login
OneSignal.login("user_internal_id_12345")

// Attributes for segmentation
OneSignal.User.addTag("plan", "premium")
OneSignal.User.addTag("city", "kyiv")
OneSignal.User.addTag("last_purchase_days", "3")

Tags are the basis for further segmentation. They should be designed in advance: 10–15 key tags are enough for most scenarios. If tags are scattered, analytics loses accuracy.

Sending via REST API

The server side is HTTP REST. Minimal request to send by external_id:

POST https://onesignal.com/api/v1/notifications
{
  "app_id": "YOUR_APP_ID",
  "include_aliases": { "external_id": ["user_12345"] },
  "target_channel": "push",
  "contents": { "en": "Your order is ready", "ru": "Ваш заказ готов" },
  "data": { "order_id": "98765", "screen": "order_detail" }
}

The data field is the payload for deep linking. On the mobile client, it is processed by OSNotificationOpenedHandler:

// iOS
OneSignal.Notifications.addClickListener { event in
    if let orderId = event.notification.additionalData?["order_id"] as? String {
        AppRouter.navigate(to: .orderDetail(id: orderId))
    }
}

Delivery and analytics

OneSignal provides delivery rate (99.9% on average), click rate, influenced opens (user opened the app within 60 seconds without clicking). For e-commerce, this is an important metric — the notification worked, but the user opened the app differently. If deeper analytics is needed, OneSignal integrates with Mixpanel, Amplitude via outcome events. For example, sending a purchase event: OneSignal.Session.addOutcome("purchase_completed") and addOutcomeWithValue("purchase_amount", 149.99). This data allows building funnels and evaluating push campaign ROI.

What is included in turnkey integration

All integrations include: detailed documentation, dashboard access, API keys, 2-hour training session, and 30 days of post-deployment support.

Timelines and how to start

Basic OneSignal SDK integration (iOS + Android or Flutter/RN), setting up APNs/FCM certificates, linking external user ID, open handler — 3–5 business days. If server-side sending logic, segment and template setup in OneSignal Dashboard is added — another 2–3 days.

Order a free audit of your current push notification architecture — it's free. Contact us for a consultation: our engineers with 5+ years of hands-on experience with OneSignal SDK and REST API will evaluate your project and propose an optimal plan. Reach out to us, and we will configure OneSignal for your stack in just a few days.

Push Notifications in Mobile App: APNs, FCM, Segmentation, Rich Push

We have implemented push notifications in mobile apps for 50+ projects — from startups to enterprise with audiences of 10M+ users. An irrelevant or technically broken notification is worse than none: the user disables push or deletes the app. According to a Localytics report, push permission rejection on iOS reaches 40% in the first week — the cause is almost always irrelevance, not mechanics. Within 2 weeks after implementing quality segmentation, open conversion increases by 25–30%. Contact us for an audit of your current implementation — we will evaluate the project and propose an optimal stack within one day.

How the Infrastructure Works: APNs and FCM

APNs is the only delivery channel on iOS. Everything else (OneSignal, Braze, Airship) is a wrapper on top of it. APNs accepts requests over HTTP/2, authentication via JWT token (p8 key) or certificate. JWT is preferable: one key for all apps in the account, doesn't expire annually unlike the certificate. For more details, see the official documentation.

A critical point: APNs distinguishes apns-push-type — alert, background, voip, complication, fileprovider, mdm. An incorrect type on iOS 13+ causes background notifications not to wake the app. We've seen projects where content-available: 1 was sent without apns-push-type: background — the app didn't receive silent push on some devices, and the team spent a month looking for an 'app bug'.

FCM on Android works through Google Play Services. For devices without GMS (Huawei, part of the Chinese market), Huawei Push Kit or a direct WebSocket is needed — a separate task. FCM supports data messages (handled in onMessageReceived) and notification messages (the system displays automatically if the app is in the background). Mixing them requires caution: if the notification block has a click_action but the deep link is not registered in the app, tapping the notification simply opens the main screen without navigation.

Why Segmentation Is the Foundation of Effective Push Notifications?

Sending to everyone indiscriminately quickly exhausts user loyalty. Personalized messages are clicked 3 times more often than bulk ones, and proper segmentation reduces churn by 25% (on one project it brought significant additional revenue per quarter). The cost of setting up segmentation in OneSignal or a custom backend depends on the complexity of filters.

Proper segmentation is built on several levels.

Topics are for broad categories: 'new promotions', 'order status updates'. User subscribes via FirebaseMessaging.getInstance().subscribeToTopic("orders"). Simple, but no flexible filtering.

Attribute-based segments — via OneSignal, Braze, or custom backend. We store in the user profile: language, device type, last activity, LTV segment. Notification goes only to those with last_active < 7_days and plan = premium. OneSignal allows building such filters in the interface without code.

Personalized — by specific device_token. It's important to store tokens correctly: the token updates on app reinstall, restoration from backup on a new phone, or resetting settings. On iOS, use UNUserNotificationCenter + didRegisterForRemoteNotificationsWithDeviceToken, save to backend on every launch, not just the first. Otherwise, after 3 months 30% of tokens in the database are outdated.

What Is Rich Push and How Does It Boost Conversion?

A standard notification with title and text is clicked less often than a rich push with image and action buttons — by 3 times. But implementing rich push is a separate task on each platform.

On iOS, rich content requires UNNotificationServiceExtension (to modify payload) and UNNotificationContentExtension (custom UI). The extension runs in a separate process with limited time and memory. If the extension crashes or exceeds the timeout, the system shows the original payload without media. A typical mistake is trying to load an image over HTTP (not HTTPS): ATS blocks the request, the extension silently fails, and the user sees a notification without an image.

On Android with API 26+, notifications are tied to NotificationChannel. If the channel is created with IMPORTANCE_LOW, sound and vibration are unavailable. Different notification types (transactional, marketing) should be in different channels so the user can disable marketing without losing order notifications. BigPictureStyle, MessagingStyle, InboxStyle are templates for expanded notifications. MessagingStyle with Person and avatars is the best choice for chats.

How to Track Delivery and Conversion of Push Notifications?

Sending a notification is half the work. It's important to know: was it delivered, opened, and did it lead to a target action.

FCM returns a MessageId on send, but does not guarantee a delivery callback — by design. For open tracking, custom logic is needed: on notification tap in onMessageReceived or via getInitialNotification() / onNotificationOpenedApp (OneSignal SDK), send an event to analytics with notification_id.

OneSignal provides built-in delivery and CTR analytics. For more detailed analysis — integrate with Amplitude or Mixpanel via webhook on open events. The budget for such a dashboard varies depending on event volume.

How We Implement Push Notifications: Typical Process

1. Audit current implementation — check token storage, update handling, notification types.
2. Design architecture — choose transport (FCM + APNs), segmentation layer (OneSignal/Braze/custom), personalization method.
3. Implementation — write registration code, inbound handling, rich push, deep linking.
4. Testing — send test campaigns, verify delivery on different devices, simulators, regions.
5. Monitoring and analytics — set up dashboard, open and conversion events.
6. Documentation and training — hand over operational materials to the team.

Typical stack: FCM + APNs at transport level, OneSignal or Firebase Notifications Composer for segmentation, custom backend for personalized event-based notifications. For large apps with >1M users, OneSignal has pricing limits — then we use Braze or a custom implementation on AWS SNS.

Timelines depend on complexity: basic FCM+APNs integration with transactional notifications — 1–2 weeks. A full system with segmentation, rich push, analytics, and A/B testing — 4–8 weeks. Order an audit of your current push infrastructure or get a consultation on implementing push notifications in your mobile app — we will contact you within a day and provide an accurate estimate.