Delegation Not Functioning for Expense Management:Expense Approval Workflow and Delegation Issue

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We are facing an issue with our expense approval workflow. Bill is defined as the top participant in the hierarchy, and we have delegated employees to approve expenses on his behalf before final approval reaches Bill.
Currently, the system triggers approvals in the following sequence:
preparer → manager → Bill
However, delegations are being ignored, and the approval flow skips the delegated employees entirely. Ideally, approvals should route to the delegated employees first before proceeding to Bill for final approval.