Developers (often called "modders") decompile the original game, inject custom code, and recompile it. The result is a modified game that bypasses the in-app purchase system.
Android users have it easy. Download an APK, allow unknown sources, and you are cheating in 30 seconds. iOS is a walled garden designed by obsessive-compulsive security architects. This makes the pursuit of the iOS IPA crack much more dramatic. subway surfers mod ios ipa cracked