Trying to add a Backblaze b2 special remote using rclone.

Have tested the remote using rclone so I know it is set up properly and connecting.

Running

git annex initremote remotename type=rclone encryption=none rcloneremotename=remotename

to initiate the remote in git-annex.

It fails with:

initremote remotename
git-annex: this rclone remote does not support empty directories
failed
initremote: 1 failed

Can not figure out what that means, searching does not help. What have I missed?