Prevent AP invoice creation when PO is rejected by supplier on iSupplier Portal

Hi, We have made it a mandate for our suppliers to accept or reject a PO via iSupplier Portal. We want to restrict the AP invoice creation on iSupplier Portal for all rejected POs. How do we go about it? Is there a profile option or can we achieve it thru Personalization?

Also need your guidance on the following: When a PO is rejected by supplier on the portal, the PO Acceptance screen should show the PO as rejected. But I can see the value in action field as 'NEW' for some newly created POs and 'Accept' for some old POs. Should we check the accepted_flag='N' in po_acceptances to get rejected POs? Please advise.