Could not resolve com.android.tools.build:gradle:3.1.4

This error message usually means that the Gradle plugin version specified in your project's build.gradle file is either incorrect or cannot be found. To resolve this error, try the following:

1. Check that you have an internet connection and that your firewall is not blocking Gradle from accessing the internet.
2. Open your project's build.gradle file and verify that the Gradle plugin version specified is correct and matches the version of Gradle installed on your system. You can check your installed version of Gradle by running "gradle -v" in a terminal.
3. If the Gradle plugin version is correct, try updating it to the latest version by changing the version number in your build.gradle file to the latest version available.
4. If none of the above steps work, try deleting your project's .gradle directory and re-importing your project into Android Studio.

If you're still having trouble, provide more information about your environment and the specific error message you're seeing.