This functionality is new as of version 4.0.
Comments and Alerts can be added to the Purchase Order via the 'Purchase Order Details' screen → 'Purchase Order Log' tab.
The user-defined Alert Type must include the 'Purchase Order' Alert Category.
To Add Comments and/or Alerts to a Purchase Order:
Navigate to the 'Purchase Order Details' screen → 'Purchase Order Log' tab.
Click the ‘Add’ button.
Type the Comment/Alert text in the 'Comment' field.
Select the 'Alert' checkbox to create an Alert.
Select an Alert Type from the 'Alert Type' dropdown list.
Refer to Configure Alert Types.
