Purchase orders get added to Events before they are invoiced. To look up a PO you'll need some other identifying information about the case.
1. Navigate to the Events page
2. Open up the filters and use selections to narrow down the field of search results and identify your event
3. It can be useful to search via Event ID or MRN # if available, using the main search. 
4. Once you've located the Event, click on its name to open the detail.
5. If a purchase order has been added, you'll find it on the Detail tab
PO Section on Mobile:
PO Section on the Web: 