Samsung Galaxy S4 (SPH-L720) “FAIL (auth)” and “SW REV CHECK FAIL” fix
These errors indicate that the phone cannot use the ROM provided (via Samsung’s ODIN loader) because the ROM is either not legitimate or is a version prior to the one currently installed. Basically, if you’ve flashed a ROM that is Android 4.4.2 (KitKat), you will not be able to revert back to an earlier version (such as Android 4.2.2).