Unlocking bootloader

Hello i have the Lg h340n and i am trying to unlock the bootloader but it fails :( i did install sdk tools and adb/fastboot and the commands work fine but this happens
When the phone is on i can find it with:
-adb devices
LGH340n1620e7f3
-adb reboot bootloader
Reboots me in to some wierd place with only commands on the top left :/
-fastboot devices
1620e7f3 Fastboot
-fastboot oem unlock
...
Failed <Remote:Unknown command>
finished. total time: 0.004s
and it sits there on bootloader doing nothing :(