Originally Posted by Jano342000
Since you are S-On I believe you have to relock your bootloader in order to run the AT&T RUU
Also to the OP, note that AT&T only voids warranty for physical or water damage. They don't care about software mods, although it is a good idea to return to as close to stock as possible before requesting warranty exchange.
RUU is a good way to do so. S-on is fine, but you have to relock the bootloader. The bootloader will then say RELOCKED instead of UNLOCKED or LOCKED. No other evidence of modding should remain after the RUU.
Please click the "Thanks" button if you found a post helpful!
Phone: AT&T HTC One (M8)
Tablet: Samsung Galaxy Tab Pro 8.4 (WiFi only)