Work Confirmation - Not showing in the LOV

Dear Community,

We're using Services Procurement - When Complex PO is approved + Payment schedule is also approved. Then the buyer would go to BWC, search for the PO # then select PO, open action LOV to create Work Confirmation, but the option isn't available, this is happening for a # of POs while other POs the option can be shown. One said, a function is missing in the resp. menu. But I am using Purchasing Super User & this option Work Confirmation can be shown on some POs.