flutter_google_map/ios/Runner/AppDelegate.swift

import UIKit
import Flutter
import GoogleMaps

@UIApplicationMain
@objc class AppDelegate: FlutterAppDelegate {

  override func application(
    _ application: UIApplication,
    didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
  ) -> Bool {
    GeneratedPluginRegistrant.register(with: self)

    // google map
    GMSServices.provideAPIKey("YOUR_API_KEY")
    
    return super.application(application, didFinishLaunchingWithOptions: launchOptions)
  }
}