Purchase Order Implemented Notification - What Are the Assigned and Expiration Dates For

Summary:

What are the Assigned Date and Expiration Dates for on the Document (Purchase Order) Implemented email notifications?

Content (required):

We've recently implemented Oracle Cloud in the last 4 months and have started getting asked about the Assigned Date and Expiration Dates displayed in the Details section of the PO Implemented notification emails that send out to buyers and requesters. We weren't briefed on these during testing and some users are concerned that their POs will expire. I'm thinking these dates pertain to the expiry of the notification itself, not the POs, but just want to get some clarity on this to relay back to interested parties.