You can send push notifications to iOS devices using the Courier's iOS SDK and Firebase by following these steps: First, you need to be an official, paid-up Apple Developer to prove your identity to iOS devices. Then, create a new project in Xcode with Swift as the language and select SwiftUI as the interface. Add the Courier iOS SDK and Firebase iOS SDK to your project using the Swift Package Manager. Set up APNs authentication key and upload it to Firebase. Link your Firebase account with the Apple Developer account. Create an `AppDelegate` class that extends `CourierDelegate` and `MessagingDelegate`. In this class, override the methods `deviceTokenDidChange`, `messaging`, `pushNotificationDeliveredInForeground`, and `pushNotificationClicked`. Finally, create a main Swift file for your app, bind it to the `AppDelegate` class using the `@UIApplicationDelegateAdaptor` protocol, and initialize the `ContentView`. Replace `COURIER_AUTH_TOKEN` with your API key and `COURIER_USER_ID` with the user ID you'd like to use for testing. Connect your iOS device to your computer, select Trust this device if prompted, and run the app on your iOS device. You can then send yourself a push notification using Courier's Quick Send feature.