Ask HN: Build a chat functionality in iOS app

I am building an iOS app and I need to build a chat functionality within the app. The app connects two people (both using the app) and I want to build the functionality to have them chat with each other in the app? What is the best way to go about doing something like this?

With my limited experience in building iOS app, I guess that this would essentially send push notifications back and forth for chat. Are there any best practices on building something which will be cheap and could scale at least decently.

Any general pointers on building this?