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.