If you have this error in Android Studio 2.3.2:

“Failed to resolve: com.android.support:appcompat-v7:27.
Install Repository and Sync Project”

Then you can add this text to your Build.Gradle file to fix it:

maven {
    url "https://repository-achartengine.forge.cloudbees.com/snapshot/"
}

This goes inside the “respositories” section, so you should find that section and make it look like this:

buildscript {
    repositories {
        mavenCentral()
        maven {
            url "https://repository-achartengine.forge.cloudbees.com/snapshot/"
        }
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:0.6.+'
    }
}

Source:
https://stackoverflow.com/questions/20574111/add-maven-repository-to-build-gradle