The delivery rate of your push notifications will not be 100%, especially when you have a large subscriber base.
Listed below are some of the common instances which lead to lower delivery rates:
Uninstalling the browser
On uninstalling the browser from the device which the subscriber used to opt-in for notifications from your store, the subscriber will simply stop receiving notifications. This is because the subscription to web push notifications is controlled by the browser on a device level. In other words, if the subscriber stops using the browser on the device he / she subscribed from, the delivery of push notifications won't be possible any longer.
Browser is not open
Push notifications are delivered straight to the subscriber's screens, even when their browser is closed. But on certain devices, the push notifications get delivered only when the browser is open on their device. When the subscriber opens the browser again, the push notification delivery will be attempted again, even if your store is not open in the browser.
PushOwl has the option of setting an expiry time on your push notification campaigns by enabling the "Do a Flash Sale" feature. If the subscriber opens their browser after this expiry time, then he / she might not receive the notification. Additionally, if the subscriber is not connected to the internet or has disabled background app refresh until the expiry time lapses, then the subscriber will not receive the notification.
Note: The default expiry time (if not specified) is 28 days.
Disabling background app activity (mobiles)
Most mobile devices have a 'low power mode' feature OR a settings options which allows people to turn off 'background app refresh'. This helps them conserve battery. Doing this might sometimes forcefully disables the background process which receives push notifications.
When the subscriber turns off the low power mode OR enables background app refresh again, the push notification delivery will be re-attempted.
Clearing site data
The delivery of web push notifications is made possible by installing service workers on the browser of the subscriber's device. On clearing the history / cache or by removing site data from the browser, the push notification subscription is removed, resulting in low delivery rate.
This is the equivalent of the subscriber uninstalling an app from their mobile device, and they cannot receive any future notifications from that app until they install it again.
Note: PushOwl automatically re-syncs the subscribers when they visit your store after they have cleared their site data, This makes them an active subscriber once again, and they will be able to receive your notifications.