Hi,
I’m trying to root the Fairphone 4, I followed https://support.fairphone.com/hc/en-us/articles/360048646311-FP3-Manage-the-bootloader and can unlock OEM in developper options
But in the part 2 I wasn’t able to get fastboot oem unlock working. Here’s the error: FAILED (remote: 'Command not supported in default implementation') fastboot: error: Command failed
I’ve tried on Windows and GNU\ Linux (version: fastboot version 31.0.2 android-tools Installed as /usr/bin/fastboot)
I was able to get it working by using Windows. The device was not recognized and had to force in Device Manager the detection of the phone as an Android device.
The command fastboot oem unlock didn’t exists had to use fastboot flashing unlock
Yeah, that’s a known problem, Fairphone haven’t gotten around to updating the documentation for the FP4 
At least the form to generate unlock codes still works 
For reference, the FP4 related article to manage the bootloader is online https://support.fairphone.com/hc/en-us/articles/4405858258961-FP4-Manage-the-bootloader