No cached version of com.android.tools.build:gradle:3.1.0-alpha03 for offline mode

Question

I have a problem in Android app, when I click build I am getting an error in build.gradle: the error message is:

"Error:No cached version of com.android.tools.build:gradle:3.1.0-alpha03 available for offline mode.
<a href="toggle.offline.mode">Disable Gradle 'offline mode' and sync project</a>"

I tried many solutions but did not work. Any idea why this error appear? My build.gradle is:

buildscript {
    repositories {
        jcenter()
        maven { url 'http://oss.jfrog.org/artifactory/oss-snapshot-local' }
        maven { url 'https://maven.google.com' }
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:3.1.0-alpha03'
        //classpath 'com.google.gms:google-services:3.0.0'
    }
}

allprojects {
    repositories {
        jcenter()
    }
}

task clean(type: Delete) {
    delete rootProject.buildDir
}