Rooting your has consequences. Read carefully:
This is the most common stumbling block for beginners. t285 root 5.1.1 cf auto root
Use the Xposed Framework to change UI elements without a custom ROM. Rooting your has consequences
You forgot to enable OEM Unlock in Developer Options. Reboot to system, enable it, and try again. t285 root 5.1.1 cf auto root
The official Samsung firmware flashing tool for Windows.