Exposing an outside folder to supervisord installation

I have mounted devices on my supervisord installation that I want to watch for things such as free space using the systemmonitor sensor. When I add the /mount/folder to the allowlist_external_dirs I get a configuration invalid and Not a directory @ data['allowlist_external_dirs'][1] when I check the configuration.

How can I get HA to view this mount path?

Anyone out there experience this before?