Knowledge base

Mobile SDKs and push: why an app needs one

You cannot send a push notification straight to a phone. Only Apple and Google can do that. A mobile SDK is the piece that connects your app, and the person using it, to the platform that wants to reach them.

5 min read · Updated June 28, 2026

Why you cannot send push directly

Mobile push is delivered through two operating-system gateways: APNs (Apple Push Notification service) for iOS, and FCM (Firebase Cloud Messaging) for Android. An engagement platform never bypasses them. It stores the device token tied to a user, builds the targeted payload, and hands it to APNs or FCM, which perform the last-mile delivery to the device.

The mental model

The platform does not send the push. APNs and FCM do. The platform owns identity, targeting, payload, and token management. The OS gateway owns delivery.

What the SDK does

The SDK is a code library you embed in the app. It handles the device-side work the cloud cannot reach:

  • Captures events: app opens, screen views, purchases. These feed segmentation and trigger journeys.
  • Registers the push token: it asks the OS for the device token and sends it to the platform, attaching it to the user profile.
  • Renders in-app and embedded messages: content shown inside the running app, which the cloud cannot draw on its own.
  • Resolves deep links: opens the right in-app screen when a notification is tapped.

Tokens are not set-and-forget

Push tokens rotate and expire. A token captured at install can go stale when the app is reinstalled or the OS refreshes it. Keeping the user-to-token mapping current, and pruning dead tokens, is an ongoing SDK responsibility. Stale tokens are a common cause of silently undelivered push.

Frequently asked questions

Can I do push without adding an SDK?

Not meaningfully. Without the SDK there is no reliable way to register the device token, attach it to a user, capture in-app events, or render in-app messages. The SDK is what links a physical device to an identity in the platform.

What are APNs and FCM?

They are the push gateways owned by Apple and Google. APNs delivers to iOS devices, FCM to Android. The engagement platform sends payloads through them rather than directly to the phone.

Why did a user stop receiving push?

Common causes are a revoked OS permission or a stale token that was never refreshed. Token lifecycle management by the SDK is what prevents the second case.

Keep reading

Channels and deliverability: getting the message there A channel is the medium a message travels on. Platforms differ less on the list of channels and more on getting one of them, email, to actually land in the inbox. Both halves matter. Customer journeys and orchestration A campaign is one message. A journey is the automated, multi-step path a customer travels, with waiting, branching, and sends along the way. This is the orchestration layer where a marketer actually works. What is MarTech? A map of the customer-engagement stack Marketing technology is just the set of software a company uses to find, understand, and talk to its customers. The jargon hides a simple shape: collect data, unify it, decide what to say, and deliver it. This is the map.

Sources

Part of the MarTech and customer engagement field notes on this site. Written by Antoni K Pestka.