On your device, go into Settings -> About and find the Build Number and tap on it 7 times to enable developer settings. Press back and go into Developer Options and enable OEM unlocking.
unlock bootloader and flash twrp
download
https://drive.google.com/open?id=1VzUS999ZS_yc6GtcKngA6GrlTpOZp2P5
Sources
https://github.com/youyim123/android_device_nubia_nx609j
unlock bootloader and flash twrp
Code:
fastboot oem nubia_unlock NUBIA_NX609J
Code:
fastboot flash recovery recovery.img
download
https://drive.google.com/open?id=1VzUS999ZS_yc6GtcKngA6GrlTpOZp2P5
Sources
https://github.com/youyim123/android_device_nubia_nx609j