Can't build project kotlin, Admob, RewardedVideoAd

[Capotasto]

There are some error in MainActivity that are very simple problem.

Admob-> RewardedVideoAd

The reposository URL: https://github.com/googleads/googleads-mobile-android-examples/tree/master/kotlin/admob/RewardedVideoExample

Executing tasks: [clean, :app:assembleDebug] in project /Users/ag0237/develop/capo/android/googleads-mobile-android-examples/kotlin/admob/RewardedVideoExample

> Task :clean UP-TO-DATE
> Task :app:clean UP-TO-DATE
> Task :app:preBuild UP-TO-DATE
> Task :app:preDebugBuild UP-TO-DATE
> Task :app:generateDebugBuildConfig
> Task :app:compileDebugAidl NO-SOURCE
> Task :app:compileDebugRenderscript NO-SOURCE
> Task :app:mainApkListPersistenceDebug
> Task :app:generateDebugResValues
> Task :app:generateDebugResources
> Task :app:createDebugCompatibleScreenManifests
> Task :app:extractDeepLinksDebug
> Task :app:processDebugManifest
> Task :app:mergeDebugResources
> Task :app:processDebugResources

> Task :app:compileDebugKotlin FAILED
e: /Users/ag0237/develop/capo/android/googleads-mobile-android-examples/kotlin/admob/RewardedVideoExample/app/src/main/java/com/google/android/gms/example/rewardedvideoexample/MainActivity.kt: (33, 5): Unresolved reference: MobileAds
e: /Users/ag0237/develop/capo/android/googleads-mobile-android-examples/kotlin/admob/RewardedVideoExample/app/src/main/java/com/google/android/gms/example/rewardedvideoexample/MainActivity.kt: (154, 11): 'onRewardedAdFailedToLoad' overrides nothing
e: /Users/ag0237/develop/capo/android/googleads-mobile-android-examples/kotlin/admob/RewardedVideoExample/app/src/main/java/com/google/android/gms/example/rewardedvideoexample/MainActivity.kt: (154, 58): Unresolved reference: adError

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':app:compileDebugKotlin'.
> Compilation error. See log for more details

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

* Get more help at https://help.gradle.org

Deprecated Gradle features were used in this build, making it incompatible with Gradle 7.0.
Use '--warning-mode all' to show the individual deprecation warnings.
See https://docs.gradle.org/6.2.1/userguide/command_line_interface.html#sec:command_line_warnings

BUILD FAILED in 2s
11 actionable tasks: 9 executed, 2 up-to-date