Identifying PO (Purchase Order) LOV empty on Create Invoice page on Supplier Portal for user with Da

Summary

Unable to create PO Matched Invoices from Supplier Portal when supplier User has Data Access restricted to Selected Supplier Sites

Content

Need:
Business need is to have supplier user accounts restricted to their own specific sites so that they only see transactions which they are allowed to see. Hence the supplier contact User Account's Data Access is restricted to 'Selected Supplier Sites' and the Purchasing and Pay sites have been added to the sites list under Data Access. Supplier users are expected to manage POs and create PO Matched Invoices from Supplier portal.

Data/Scenario:
Supplier has one purchasing site (PUR1) and multiple pay sites (Pay1, Pay2, Pay3 etc.).