Organization membership rule via API

Hello, I am trying to set membership rule for "Organization" entity in OIM 12c using API, but getting the below error.

The purpose of the rule is to have "Users" dynamically attached to the "Organization".

Through OIM Identity Console, the same rule can be created fine for the Organization 

(usr_emp_type = Agent)

Remember that this is an OOTB user's attribute not organization's attribute, and Identity Console allows you to pick User's attribute when creating the rule for the Organization

Through the API, we are getting an 'Attribute does not exist error' for ANY OOTB USER ATTIBUTES. Could you please help me identify why this is failing?