How to use properly the GRUB payload?

[Ioannis Koutras]

Hello,

I have just flashed coreboot (git commit: 89e7b49) on a Lenovo X220 with
GRUB2 as payload and when I boot the machine, I am getting GRUB's command
line.

I am trying to boot a systemd-boot (previously known as gummiboot?)
payload from my disk partition, but I am getting unrecognised payload. Any
idea what's the issue there?

Additionally, could anyone help me set it up properly, as in searching for
grub.cfg in disks and looking to boot from USB?

Many thanks in advance,

Ioannis