The version "macOS 10.13.99" does not officially exist. This specific number often appears in error messages when you try to install iTunes on a modern Mac (macOS Catalina or later), as those versions require you to use the Finder or Apple Music app instead of a separate iTunes download.
: If you already have it installed, you can typically update it via the Updates tab in the Mac App Store . macOS High Sierra (10.13.6) System Updates itunes macos 10.13.99 download
If you deleted the app and try to redownload it, you may find that the App Store tries to force you to upgrade to Catalina or newer. To get iTunes back without upgrading your OS: The version "macOS 10