Basically these are two different things, REST access to the filesystem (aka Namespace API)

and access to system configuration and statistics (aka Platform API, PAPI)

Both are described at length in https://support.emc.com/docu66301_OneFS-8.0.0-API-Reference.pdf?language=en_US

A very quick how-to for setting up privileges for the filesystem API is here:

Isilon: AEC_FORBIDDEN received doing API call

A concise list of privileges for the system configuration API is somehow missing

from the above API Reference document, but can be found starting from page 137 in

the regular Web Admin Guide https://www.emc.com/collateral/TechnicalDocument/docu65068.pdf

hth

-- Peter