I am an iPhone app coder, and I\'m using Firebase as my backend server. Firebase doesn\'t support Push Notifications, so I\'ve been trying to figure out how to include them
There are a couple of options: (well, more than a couple but here's two)
Parse handles push notifications very very well - they have that down pat and it's super simple. However, you may have issues with users and accounts - depending on what your app does.
You mentioned Pushover. We worked their API a while back but not through Zapier. If I remember correctly, I believe you can simply register your app, send an HTTPS: request to their server and then the notifications are sent from/to your app.
Also, you may want to evaluate how you are using push as it's possible you can roll a notification-like event just into the app itself.