import kotlinx.android.synthetic.main.activity_main is not working

Check "build.gradle(:app)" file,

plugins {
    id 'com.android.application'
    id 'kotlin-android'
}

if kotlin extension is missing, add kotlin-android-extensions as shown below and click on "Sync now"

plugins {
    id 'com.android.application'
    id 'kotlin-android'
    id 'kotlin-android-extensions'
}

Can you try

• File | Invalidate Caches / Restart
• Deleting .idea folder
• Clean
• Re-import the project

OR just remove apply plugin: 'kotlin-android-extensions' , sync gradle plugin and then I added it again.