Once the PO has been submitted, there must be an approval in within the policy workflow. 

1. Spend Management > All > Approval Workbench

2. If edits are needed, select edit and it will take you to this screen to complete those: in this screen, you will have access to approve or decline

3. Locate the PO and review the details and attachments. Once reviewed and if no changes are required, check the box and then select approve.