An approver can approve the requisition, which that approver previously denied. Is that expected?

Following are the steps followed by the user:

1. Submit a requisition.
2. Log in as first approver, and click Deny.
3. Open the same requisition again and click Approve.
4. Approver can approve successfully.

An approver who initially denied a document can return to the document, later, to approve it, which reactivates the approval process. In this situation, the Ariba Spend Management application continues with the existing approval flow without re-evaluating the approval rules.

This behavior is controlled by Application.Approvable.AllowApprovalOfDeniedApprovable which is turned off by default.

Core Procurement > Core Administration
Core Procurement > Core Administration > Approval Flows