Upon trying to install Parallels Desktop 18 on a Mac with macOS High Sierra 13 you might notice that Parallels Desktop 17 build has been downloaded. It's not a mistake but our sincere intention to help you. Based on system requirements, Parallels Desktop 18 can't be installed on Mac computers with macOS High Sierra. As a result, we install the latest Parallels Desktop version that is compatible with macOS High Sierra 10.13.x.
You may activate Parallels Desktop 17 with your Parallels Desktop 18 key and enjoy our product. Activation instructions can be found in KB 124225.