Gradle sync failed: Sync failed: reason unknown

99% of the probability is the problem of Android SDK
C: \ XX \ appdata \ local \ Google \ androidstudio2020.3 \ log
analyze the log of the studio and find it

com.android.tools.idea.gradle.project.sync.idea.issues.SdkPlatformNotFoundException: Module: 'libzxing' platform 'android-28' not found.

Just download another android-28 SDK

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