Gradle sync failed No cached version of com.android.tools.build:gradle:x.x.x available for offline mode

This is one of the most common Android Studio error :

No cached version of com.android.tools.build:gradle:x.x.x available for offline mode

Reason :

Your gradle offline mode is enabled. You need to turn if off. Otherwise android studio will not download a new gradle version if it is not available locally.

How to turn off offline mode :

Click on the Gradle window on right side of your Android studio. Then, click on the offline sync enable/disable button. I am marking it in the below image :

I am using one theme for my Android Studio. So, it will look bit different on your system. You can hover on a icon to find out what it does.