Storage Box Hetzner via SSH

Storage Box from hetzner.com are a cheap option to create remote backups it supports rsync via SSH but I can't make it work.

Anyone have already tested it? If I ran on the server the rsync command it connects to the storage box, but I have tried both the regular and the new backup system an can't connect.

I think the SSH connection to storage box it's really limited it only can be done directly from the rsync command something like this:
rsync --progress -e 'ssh -p23' --recursive <local_directory> <username>@<username>.your-storagebox.de:<target_directory>

Documentation here - https://docs.hetzner.com/robot/storage-box/access/access-ssh-rsync-borg

I'd like to enable the new backup system using incremental backup via SSH, I thought it use rsync command but probably it try to connect first to do something and it fails.
Any help?