Hetzner box storagebox suppports "rclone serve restic --stdio"

from the terminal, if i run help, i get the following output

Available as server side backend:                                             |
|   borg                                                                      |
|   rsync                                                                     |
|   scp                                                                       |
|   sftp                                                                      |
|   rclone serve restic --stdio                                               |

so far, no documentation from hetzner, except for a hetzner forum post in german.
and the setup is complex, at least to me.

the problem is that rclone version does not work, do not know what version of rclone yet.

from what i understand via google translate, the main advantage is --append-only
whereas, sftp server does not support.

Rclone can be used on the Storage Box to create backups via Restic and store them in an append-only repository. For this purpose, an SSH key with a forced command must be stored in the ".ssh/authorized_keys" of the Storage Box.

so far, not working, and not sure if the issue is https://github.com/rclone/rclone/issues/6646

+ export RESTIC_PASSWORD=password
+ restic -o 'rclone.program=ssh -p23 u00000@u00000.your-storagebox.de forced-command' -r rclone: init
Fatal: create repository at rclone: failed: error talking HTTP to rclone: exit status 8