Choosing a provider

• FCM Free, flexible, first-party for Android; requires manual dashboards/segmentation.
• OneSignal: Faster to market with UI dashboards, segments, A/B testing, and analytics.

iOS (APNs) essentials

• Certificates/keys must match bundle identifiers and entitlements.
• Provisional Authorization can improve opt-in rates by soft prompting.
• Delivery can be throttled in Low Power Mode or Focus modes—monitor notification service extension logs.

Android specifics

• Define notification channels by importance to avoid user silencing.
• Handle data-only vs notification messages—render your own notifications for consistency.
• Foreground service requirements for long-running tasks.

Recommendations

If you need speed, dashboards, and experimentation: OneSignal. If you prefer full control, low cost, and custom pipelines: FCM.