Unable to boot GuixSD USB stick

[良ϖ]

Hi,

I've followed instructions on this page:
https://www.gnu.org/software/guix/manual/html_node/USB-Stick-Installation.html#USB-Stick-Installation

everything goes smoothly and at the end I get a partition named
"gnu-disk-image" with flag "boot". Sounds good. When I mount it it's a
classical GNU / Linux root with folders bin, root, dev, etc, gnu,
home, mnt, root, run, tmp and var.

However when I reboot the key isn't recognised by my laptop so I'm
unable to install it :'(

Any ideas how I could solve that?

Thanks in advance,

piotr