We send push notifications from our apps ourselves, from our own servers — no third-party messaging service is involved. When you allow notifications, the app registers its device push token with us, together with the app and its version, the operating system, your timezone and approximate country, whether notifications are switched on, and — if you are signed in — your account. We keep it until the app stops reporting in or you switch notifications off.
To reach your device, each notification is handed to the platform's own delivery service: Apple Push Notification service (APNs) on iPhone and iPad, and Firebase Cloud Messaging (FCM) from Google on Android. That is the only way a notification can be delivered on those platforms. Data shared: the device push token and the notification itself (its title, text and link).