Cracktool4 would "inject" a custom dylib (dynamic library) into the IPA. This library acted as a middleman, intercepting calls to the app's server and returning a "Success" or "Pro" status. The Sideload:

: It is surprisingly user-friendly, offering a list of supported apps and a simple toggle to apply or revert patches. Why Users Seek the IPA Version

While the tool is popular for accessing "free" software, it carries substantial security and ethical risks: Malware Exposure