This functionality is new as of version 4.0.
When receiving Deliveries, the Purchase Order Items that are in the Delivery, must be added to the the 'Delivery' tab.
Purchase Order Items can be added to a Delivery one at a time; or, by clicking the ‘Add All Items’ button.
Refer to Add Delivery Item.
To Add All Purchase Order Items to a Delivery:
Navigate to the 'Purchase Order Details' screen → 'Delivery' tab.
If a Delivery that has not been completed is not available, click the ‘Start New Receiving’ button to add one.
Clicking the ‘Add All Items’ button.
This will add all Purchase Order Items that have not already been received, to the Delivery.