Another solution that I would like to add:

Knowing that the Push Notifications prompt appears only once, we can add an alert before even triggering the prompt.

For example, when the user launches the app we can show an alert that says "Enable Push Notifications?" with 2 buttons (Ask Later and Yes).

1. If the user clicks on Ask Later, we will show the same alert after n app launches and so on until the user clicks Yes.
2. Upon pressing on Yes, we will then present the Push Notifications prompt.

I believe that this method is quite beneficial (at least for me) for having a bigger percentage of registered users.