I was encountering the worst of errors with a brand new react-native android project :
“Gradle sync failed: Sync failed: reason unknown”
Luckily, I found the reason – I am using the latest Android Studio Arctic Fox and thought to check the SDK that is installed by default… voila
it’s using Android 12 preview – this doesn’t play well with the current react-native version at time of writing (0.64.2).
Simply install Android 11 then re-sync your gradle files and this error will disappear!
Hope that helps!