Hey, we’re developing an invoice approval solution. We sent multiple reminders to users when they have open approvals:

1. A daily email digest that gets send in the morning when you have open approvals
2. A mobile push notificaiton on every new invoice approval request
3. A mobile push notification where you can be @mentioned
4. An email for @mentions
5. etc.

We want to learn how users are coming to our app. Are the notifications working? I think for the emails we can use the referrer parameter. But what about push notifications?