It will probably be clearer if you use the same name for the folder in EagleFiler and the folder that it’s linked to.
Do you really want to have EagleFiler manage your Downloads folder? I’m not sure that makes sense because whenever you move a downloaded file you’ll be violating the Rules for Library Folders. I guess I don’t understand—big picture—what your goal is here.
It doesn’t look like you created a Documents folder in EagleFiler first. Also, it’s not clear me what you did (which Terminal command you entered) or what failed (was an error reported?).