404 message when invoking appmode

I have anaconda on linux installed and enable appmode. when pressing the appmode, I correctly get the page displayed.
now did the same installation on another server and running the same notebook, pressing the appmode, returns a 404 message. I run the notebook directly from the linux machine where anaconda/jupyter was installed. jupyter has been restarted after enable
(base) root@eva:~# jupyter nbextension enable --py --sys-prefix appmode
Enabling notebook extension appmode/main…
- Validating: OK
what could be the reason - difference between both machines ?
thanks for all info, best regards, Guy