You wish to recognize the revenue of the PO immediately: as soon as the invoice is generated. Journal entries are created.
Deferred
The invoice is generated. However, the revenue is considered deferred or unearned. Deferred revenue is a liability. It is recognized proportionally as revenue as you deliver the promised service or product to your customer over time.
Unbilled
The invoice has not been generated. However, the service or product has been delivered. This is applicable in postpaid use cases only.
