Unable To Reserve Standard Purchase Order

HI

I'm trying to test workflow for which I need to raise a PO and verify.

Requirement:

1) Buyer raises PO and it should route to PURCHASING MANAGER.

2) After PURCHASING MANAGER. approves if the PO<$10,000 then it should route to Director of Purchases if PO>$10,000 it should route to Chief Admin Officer.

3) After the Action the buyer should receive a notification that is approved/Rejected.

Current Flow:

Raised PO and it went to PURCHASING MANAGER and then it currently being routed to Director of Purchases and then after his approval it is being routed to Chief Admin Officer irrespective of Amount.