cat /etc/btrbk/btrbk.conf
volume /btrfsroot
subvolume @
group root # Matches the group configuration option of volume, subvolume or target sections.
snapshot_dir snapshots_root # Create snapshots in /btrfsroot/snapshots_root
subvolume @home
group home
snapshot_dir snapshots_home
target send-receive ssh://test.local/backups/snapshots_home
But it doesn't seem to be working.