I first tried with invalidate cache/ restart option but it doesn't help me.

When I updated Kotlin to 1.1.60 in project's gradle file, problem is solved.

Also, use this in app's gradle for stdlib

implementation "org.jetbrains.kotlin:kotlin-stdlib:1.1.60" 

instead of

implementation "org.jetbrains.kotlin:kotlin-stdlib-jre7:1.1.60"

In Android Studio, click on File -> Invalidate Caches / Restart... , then select "Invalidated and Restart". This solved my problem.

This error also occurs if you have the mavenCentral() repository missing in allprojects. Your build.gradle (:app) should contain at least this:

allprojects {
    repositories {
        google()
        mavenCentral()
    }
}

jcenter() would work as well (for now), but that repository reached end-of-life and shouldn't be used any more.

Important Update

You should check JDK version before setting config

Kotlin gradle config page has detailed information about this.

Step 1

Check kotlin version in project level gradle file.

classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"

For kotlin_version '1.2.x' Use jdk NOT jre

Step 2

Check JDK version in File > Project Structure

Or check in build.gradle

compileOptions {
    sourceCompatibility JavaVersion.VERSION_1_8
    targetCompatibility JavaVersion.VERSION_1_8
}

If no JDK version is set in Project Structure, then choose by Android Studio version

• JDK version is 1.7 for Android Studio Version < 2.2.1
• JDK version is 1.8 for Android Studio Version < 2.2.1

Because Android Studio is bundled with jdk 1.8 since 2.2.1 version.

You have 3 options of kotlin stdlib, choose according JDK version

implementation"org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version" //jdk_version == 1.8
implementation"org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version" //jdk_version == 1.7
implementation"org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version" // jdk_version is < 1.7

if kotlin version is'1.1.x' Use jre NOT jdk

implementation"org.jetbrains.kotlin:kotlin-stdlib-jre7:$kotlin_version" // or jre8

Update Kotlin Version?

You can update Kotlin version from Tools > Kotlin > Configure Kotlin Updates

Kotlin-stdlib-jre7 is deprecated since 1.2.0 and should be replaced with kotlin-stdlib-jdk7

implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version" 

just delete .idea folder from project,and run android studio again, it will resolve KOTLIN NOT CONFIGURED issue.

A common reason of the "Kotlin Not Configured" message is an internal Android Studio exception due to a bad plugin. In order to fix that you should disable the bad plugin.

When such plugin crash occurs, on the "Wellcome screen" you'll see a small notification (see illustration image) where you can click it and disable the bad plugin:

None of the other solutions solved my problem. I ended up figuring out that the problem lied in the google services version. Just update it to the latest.

Top level gradle at dependencies:

classpath 'com.google.gms:google-services:4.1.0'

In my case, after the update of Android Studio and plugins, I could create new projects, but my old projects were having "Gradle Sync Issues".

The solution was in File/Project Structure.../App/Dependencies:

implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version" 

And then I just updated the Kotlin version in my project build.gradle:

From:

ext.kotlin_version = '1.2.30'

To:

ext.kotlin_version = '1.3.21'

Then I tried Sync again.

Obs: You can check your Kotlin version in Tools/Kotlin/Configure Kotlin Plugin Updates

I have tried all above solutions but non of them works for me.

Then finally I got success with below solution, so it may helpful for some one like me.

1. Delele all .iml files (in root project, libraries and modules)
2. Rebuild project

In my case I had to update Android studio from version 3.4.1. to 3.5 and it resolved the kotlin not configured error.

Delete .AndroidStudio3.6 folder in C:\Users\Username and re-open Android studio works for me

The only fix for me was adding

apply plugin: 'kotlin-android-extensions'

in build.gradle (:app)

One other point to check is version of your Gradle in gradle-wrapper.properties, if you use one.

Make sure that distributionUrl=https\://services.gradle.org/distributions/gradle-4.1-all.zip

Has version 4.1 or higher.

You may also have the following in your build.gradle:

task wrapper(type: Wrapper) {
    gradleVersion = '4.1'
    distributionUrl = "https://services.gradle.org/distributions/gradle-$gradleVersion-all.zip"
}

Where Gradle version is lower that 4.1

Though I see that the question already has answers that work, one might also try the following solution.

Right click on the file name (Main.kt) -> Run 'Main.kt'.

This will download a gradle file from the gradle.org website.

Wait for it to unzip. The errors were cleared.

In my case, it was a broken update of one of the plugins I've used. Check your error logs from Android Studio this will lead you to what is the problem.

Simply Create a new Activity and select its language to kotlin Android studio Automatically configured kotlin for you.