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.
However, if you need , here is the correct information: itunes macos 10.13.99 download
Even when downloading the correct iTunes 12.8.3 for macOS 10.13.6, you might encounter issues. Here is the troubleshooting guide: The version "macOS 10