Cannot switch from mode 0x3 (U2F only)

[agoode]

$ ykneomgr -M 3

$ dmesg
[1278579.887437] usb 1-9.4.4: USB disconnect, device number 118
[1278580.832066] usb 1-9.4.4: new full-speed USB device number 119 using xhci_hcd
[1278580.917717] usb 1-9.4.4: New USB device found, idVendor=1050, idProduct=0402
[1278580.917719] usb 1-9.4.4: New USB device strings: Mfr=1, Product=2, SerialNumber=0
[1278580.917721] usb 1-9.4.4: Product: Yubikey 4 U2F
[1278580.917722] usb 1-9.4.4: Manufacturer: Yubico
[1278580.919731] hid-generic 0003:1050:0402.01AC: hiddev0,hidraw6: USB HID v1.10 Device [Yubico Yubikey 4 U2F] on usb-0000:00:14.0-9.4.4/input0

$ ykneomgr -M 6
error: ykneomgr_discover_match (-4): Backend error

$ lsusb
Bus 001 Device 119: ID 1050:0402 Yubico.com

[agoode]

This page explains it best: https://developers.yubico.com/libu2f-host/Mode_switch_YubiKey_NEO.html

Maybe the readme could copy this info.