[ReactNative] Android gradle build failed

[RUN_GRADLEW] * What went wrong:
[RUN_GRADLEW] A problem occurred configuring project ':expo'.
[RUN_GRADLEW] > com.android.builder.errors.EvalIssueException: compileSdkVersion is not specified. Please add it to build.gradle
[RUN_GRADLEW] * Try:
[RUN_GRADLEW] > Run with --stacktrace option to get the stack trace.
[RUN_GRADLEW] > Run with --info or --debug option to get more log output.
[RUN_GRADLEW] > Run with
[RUN_GRADLEW] --scan
[RUN_GRADLEW] to get full insights.
[RUN_GRADLEW] ==============================================================================
[RUN_GRADLEW] * Get more help at
[RUN_GRADLEW] https://help.gradle.org
[RUN_GRADLEW] BUILD FAILED in 49s
[RUN_GRADLEW] 10 actionable tasks: 10 executed
[RUN_GRADLEW] Error: Gradle build failed with unknown error. See logs for the "Run gradlew" phase for more information.

에러 해결

compileSdkVersion 이 명확하지 않아서 그런가 싶어서 일일이 다 지정도 해줬는데도 안 되길래 찾아보니

android 폴더 하위에 local.properties 가 없는 걸 보고 만들어 줬더니 된다.

android/local.properties
sdk.dir=/Users/{YourName}/Library/Android/sdk