If you are downgrading from a newer version of iTunes to an older one, you might see an error stating that your iTunes Library.itl file cannot be read because it was created by a newer version.

If you are using a modern Mac running macOS Catalina, Big Sur, Monterey, Ventura, Sonoma, or newer, [3]. Instead, use these built-in alternatives:

Connect your iPhone or iPod to your Mac and open Finder [2]. Your device will appear in the sidebar, allowing you to sync music, backup, and restore just like you did in iTunes [2, 4].

If Apple has removed the specific build you need, reputable software archives still host them:

iTunes 10 was one of the last versions to feature "Cover Flow," a highly aesthetic, visual way to browse through album artwork that many users still miss.

iTunes 10 was designed for older Mac operating systems like Mac OS X Snow Leopard, Lion, and Mountain Lion. It will not run natively on modern macOS versions (macOS Catalina and newer) [3]. How to Download Older iTunes Versions for Free

To give you the most accurate solution, could you tell me you are currently running and which Apple device you are trying to connect? I can then guide you to the exact software you need.

When searching for the specific version "10.1.3.99", it is important to clarify a few technical details regarding Apple's software versioning: