There are a couple of issues that affect the Purchase order not showing in WMS.
1. 7-month window:- WMS Replicates 7 Months worth of Purchases, once a purchase order is older than 7 months it is marked as Closed.
If you need to receive an order outside this period, you may change the date in an Accounting system and replicate to recreate the purchase or use the check-in function.
2. Replication cut off date: There is an option in WMS preferences for the select replication start date for purchases. To find which date, Go to Options > Preferences... > Replication tab
3. Hide Closed Records: If your purchase is hidden, then check the Hide CLOSED records: Options > Preferences... > in the General Tab