I can't unlock bootloader on fly fron linux

My OS is majaro linux.

My phone is fly nimbus 8.

I tried to unlock bootloader on it.

I followed the instruction.

First I go to the Dev mod then enable OEM unlock and USB debugging.

Second I typed:

adb devices

output:

List of devices attached

56090913288827  device

Then I typed:

adb reboot-bootloader

It became like this:

Then I checked again:

fastboot devices

output:

56090913288827  fastboot

It seems all works out good!
But then I entered:

sudo fastboot oem unlock

And then nothing. I mean absolutely nothing: it does not throw an error, not answers, not completes.

By the way, the phone does the same - absolutely nothing!

if I plug off the device it writes:

FAILED (Status read failed (No such device))

fastboot: error: Command failed

I tried it already ten more times but it doesn't want to work!

Does anyone know what the problem?

Did somebody have the experience in flash the fly(in particular nimbus 8)?

I'll de be waiting for an answer!

Thanks!