When adding the Super Compliance Officer (SCO) or Compliance Officer (CO) role to a specific user via API, the following error message may be displayed.
This error means you are trying to add the SCO or CO role though the user already has that role assigned to them. If you would like to demote or promote the user, you need to remove the role they currently have first and then assign the new role.
Read the Remove User REST API page to learn how to remove a role from a user.