A single purchase order can have its ordered contents delivered in multiple parts. Each delivery moment produces a delivery object. The aggregated delivery objects are a grouped overview of all deliveries for a purchase order.
An aggregated delivery instance is created automatically when the first delivery happens.
Aggregated deliveries, deliveries and purchase orders are different entities
These objects don't share the same IDs.
A common use case is to retrieve the aggregated delivery object of a purchase order. To do this, use the query param filters that filter on the aggregated delivery's purchase order instead of including the purchase order's ID in the URL.