GL Approver Restriction

Problem Statement: A user has been assigned the role to create manual journals. Once the journal is submitted, it is routed to their manager for approval. The manager is currently able to approve the journal even though they do not have the GL approver role. However, from a business perspective, the manager should not be authorised to approve GL journals.

Expected behaviour: The system should prevent the journal from being routed to the manager for approval if they do not hold the appropriate GL approver role.

Could you please advise on how we can enforce this behaviour?