In Android 5.0 to Latest Android Versions there is a check box in Developer Options that enables the OEM unlock command to work.

 If that box is not checked, then an error occurred during the bootloader unlock process.

Both Android versions 5.0 to latest came with the “Enable OEM unlock” options.

Developer Options are hidden, so you will need to make those appear in Settings. 

To get Developer Options then go  into Settings>About phone, and tap on the “Build number” around 7-8 times until it confirms that you are now a “Developer.”  

Go back to the Settings list and you will see “Developer Options” in Settings.

“OEM unlock,” is a part of the command used to unlock Android phone’s bootloader.