Reminder: On iOS there is a separate process (called a notification service extension) that handles receiving payments if the Phoenix app is in the background or isn't running at all.

The previous architecture did NOT do a good job displaying notifications IF multiple payments were received at the same time.

For example: if you send 2 payments to the same wallet at the same time, the receiving device will display a generic push notification that says "multiple payments received" (which is not ideal). Furthermore, if our server sends multiple push notifications to the device, then a second notification will be displayed that says "missed incoming payment" (which is incorrect).

This PR fixes the problem. Now the device will always display a separate push notification for each received payment. Which is more inline with user expectations. Also, if the server sends multiple notifications, they are handled properly by the device.

Technical details:

A "notification service extension" is designed to modify the content of a single remote push notification. However, it's also allowed to add or remove from the list of local notifications.

So if 2 payments arrive while processing a notification then:

• it updates the remote notification with info from payment 1
• it creates and displays a local notification with info from payment 2