One impression is one subscriber successfully receiving one push notification.
The delivery rate of push notifications is never 100%. If you have 1000 subscribers and send a push notification campaign out to all of them, PushOwl will attempt to send your campaign to every subscriber, but because of different limitations, a handful of these subscribers won’t receive your notification. This is why we don’t measure by the number of push notifications sent but, by their success.
Why is our pricing based on Impressions?
Since all your subscribers won't receive your notifications, it doesn't make sense to count the undelivered numbers towards your monthly quota.
Let’s say you have a base of 1000 subscribers, and we charged you by the number of notifications you tried to send. If you were to send a campaign to your subscribers, and only 600 of these subscribers received your notification, it would be unfair to charge you for attempting to send 1000 notifications.
As you keep sending multiple campaigns every month and as your subscriber base grows, this number of undelivered notifications would just keep growing. Essentially, you'll be paying for notifications that create no impact.
However, PushOwl tracks your notifications based on impressions, charging you only when a subscriber successfully receives the push notification. Simply put, you pay only for notifications which are delivered.
TL;DR: We only put a price on success.