Unfortunately, . The final version of macOS High Sierra was 10.13.6 . Apple’s version numbering never reached .99 for that release.
Uninstall your existing broken or old iTunes. itunes macos 10.13.99 download
Requests for "10.13.99" often appear in search queries because of a confusing error message some users see on the Apple Support Community which states an update requires "version 10.13.99 or earlier". This is typically a system error and does not mean that version exists. macOS 10
However, there is a crucial technical detail you need to understand before clicking any download links: macOS 10.13.99 does not exist Unfortunately