To install an IPA on iOS 4.2.1, your device typically needs to be jailbroken to allow the installation of unsigned or "sideloaded" applications.
This is the most reliable source for verified, original IPAs. You can find Version 1.0.1 and Version 1.2.1 hosted here. Subway Surfers Ipa Ios 4.2.1 BETTER Download
Use a legacy version of iFunBox or a similar tool on your PC to drag and drop the IPA file onto your device. Why Version 1.2.1? To install an IPA on iOS 4
Use tools compatible with iOS 4.2.1 (like GreenPois0n or Redsn0w). Use a legacy version of iFunBox or a
On platforms like Reddit's r/LegacyJailbreak , users share modified IPA files where the MinimumOSVersion in the app's metadata has been changed to 4.2.1 to bypass the installation block. How to Install on Legacy Devices
Install "AppSync for iOS 4.0+" from a legacy Cydia repository to enable IPA installation.