Did some extra research but still confused

I answered some of this here: Load JSON data into a PDF file on an iOS app (saw it first). Essentially, you’ll need a server/service running somewhere (outside of your mobile application, as it needs to be running 24/7 for it to be effective) that would be listening for webhooks. Ideally, we also strongly discourage calling any of Square APIs directly from the mobile application itself as this means you would be storing your secret access token in the application which is a security risk. Anything doing with our APIs should be coming from a backend server.

At a very high-level, this could look like:

  • Your mobile application wants to start a Terminal checkout via a button. On button click…
  • Your mobile application makes a HTTP request to your own server/service
  • Your server/service receives the request, understands you want to make a new Terminal Checkout, and calls CreateTerminalCheckout with whatever parameters you need (probably want to pass the amount from your mobile application for example).
  • Once your server makes the request, your terminal would be ready for payment
  • Customer pays on the terminal
  • Your server/service receives a payment.created webhook
  • Do something with the webhook (i.e notify your mobile application that the payment was complete)