Hello,
I am Georg, and I am also new to XCP, kind of...at work, we have XEN, but sadly, thats not my business.

Long story short, I got nearly everything sorted out, but not USB passthrough.
I got all devices showing up in XCP-center, and attached them to the VM.

When I start the VM, all USB devices are attached. But as soon as the VM is booting, the status "Attached" changes to "No".
[VM -> Properties -> USB]

However, what I found out: for example, I attach my keyboard and pass it to my Windows vm: then why I can control the local XEN console with this keyboard I passed through?

And this error:
"Failed","Starting VM 'Windows 10 (64-bit) (1)'
Internal error: xenopsd internal error: Call to usb reset failed: Forkhelpers.Spawn_internal_error("usage: usb_reset.py attach [-h] -d DOMID -p PID [-r RESET_ONLY] device\nusb_reset.py attach: error: argument -r: expected one argument\n", "", _)
Time: 00:00:23","xcp-ng","Jun 29, 2019 12:05 AM"