How to get the commercial invoice of a shipment

https://api.easyship.com/2023-01/shipments/{easyship_shipment_id}

I am reading about the above url and the part about commercial invoice says "An invoice will only be provided if necessary. Some couriers offer a paperless invoice service". What exactly does it mean "if necessary"?

Is there an api endpoint that allows me to get the commercial invoice of a shipment regardless?