I know this is a common issue, I haven't found any clear information anywhere I've looked though. I've got a M919 S4 that was OTA upgraded to 4.3 with MK2 baseband. Still stock, still unrooted. I ordered an unlock code from unlockcodesource, they give three codes to attempt, all of which failed. In the past, we would simply downgrade from 4.1.2 to 4.1.1 with Odin and navigate to the UMTS menu and unlock from there. Now after the 4.3 upgrade with knox, all codes are failing and I obviously can't use the UMTS menu trick because it only works on 4.1.1.
Does anyone know of some not so simple methods to downgrade without bricking? Can I root, flash a custom earlier version image and earlier bootloader, and flash the stock 4.1.1 image over that? I've heard that knox won't even allow flashing custom recoveries, I'm pretty comfortable with ADB so that shouldn't be an issue.
If none of this is possible, anyone know a way to get any Samsungs with knox to accept unlock codes?
Thanks in advance guys