Please configure Android SDK

FIX FOR 3.1.2 OR NEWER VERSIONS

I faced the same issue on Android studio 3.1.2, but a simple Sync didn't work for me.The solution was a bit different: I go to

1. File -> Invalidate Caches -> Invalidate

2. File -> Close Project.
3. Remove the project from the Android Studio project selector window.
4. Quit from Android Studio(X)
5. Start Android studio and open project again

After changing Build Tool Version on the pop screen

 26.0.1 changed into 26.0.3   // else selected the highest available version

then click OK started working for me...

(or)

Simply Restart Andoid Studio File->Invalidate Caches and restart