Unlocking Bootloader Android 7.1.2
Enable OEM Unlocking
If your devices manufacturer allows OEM unlocking
A.K.A (Also Known As) "Bootloader Unlocking".







After Enabling OEM Unlocking    


Reboot to Fastboot   

ADB


adb reboot bootloader

OEM Unlock   


fastboot oem unlock
or
fastboot oem unlock -go
or
fastboot oem unlock /path/to/unlock-token.bin    



If you have an MTK CPU you might be interested in flashing image's using a scatter file and SP Flash Tool v5.16 or above, as it doesn't require an unlocked bootloader.