Integration

We are trying to create employees as suppliers and assign bank account to the supplier using REST API (/fscmRestApi/resources/11.13.18.05/instrumentAssignments) via OIC integration. We are getting Access invalid error even though the integration has supplier manager and supplier administrator roles.Is the integration user required to an employee/procurement agent to assign bank accounts to suppliers at site level or is there any way to get through it without making the user and employee or contigent worker?