B2B order approval process, buyer place an order, how to approve order by approver in different business unit?

B2B order approval process, buyer place an order, how to approve order by approver under different business unit? do we need customization ? this is for Medical B2B order case. buyer- doctor, approver- insurance company . They are different business units in backoffice , approver and doctor have m:n relationship . please give help ! Thanks in advance.