Sugar On-Demand: New User Creation via API

Hi,
    I am working on a client requirement that is to create new user in sugar on-demand via api.
I am trying to create user on my sandbox sugar via postman but i am getting not_authorized error. While if i do GET POST api calls to other module(Accounts,Contacts) i am getting results. 

Are there any cloud settings that need to set to enable user creation via api.

Please let me if anybody has any idea.

Regards,

Shameen