Getting 'The user is not authorised to access the resource' as response

Summary

When I am trying to call the end points adminAccessRights, accessRights and roles, I am getting 'The user is not authorised to access the resource'.

Content

I need to limit the access control of internal users and shoppers.But when I am trying to call the end points adminAccessRights, accessRights  and roles to create custom access rights and roles, I am getting 'The user is not authorised to access the resource' as response. I am using a demo instance now, is that the reason for this?