Install Xcode

If your Mac OS is running Mojave, you will need to install Xcode.

Install Xcode from this website.
Accept the Terms and Conditions.
Ensure that the Xcode app is in the /Applications directory. Do not put it in /Users/{user}/Applications).
Point xcode-select to the Xcode app Developer directory using the following command:

  sudo xcode-select -s /Applications/Xcode.app/Contents/Developer

Note: Make sure your Xcode application path is correct.

Xcode: /Applications/Xcode.app/Contents/Developer
Xcode-beta: /Applications/Xcode-beta.app/Contents/Developer