with U3 firmware on Android 8.0 Oreo, you must unlock the bootloader, install a custom recovery like TWRP, and then flash a root package such as Magisk.

To root a Samsung Galaxy A3 (2017) model Go to product viewer dialog for this item.

: Rooting will permanently trip the Knox counter, voiding your warranty and disabling features like Samsung Pay and Secure Folder.

: Flashing incorrect files for the wrong binary version (U3) can permanently brick your device.

: Unlocking the bootloader and rooting will perform a factory reset, erasing all data.