Your invoicing software issues the invoice (SmartBill first, then Oblio, in Romania) through the connector, at the moment chosen in Settings: at packing, after the parcel is verified by scanning, or at order confirmation.
The default is at packing, so the invoice reflects exactly what ships; if an item is missing or the size changes, the invoice comes out right.
Invoicing connectors are in progress. Until then, issue the invoice in your software and add its number to the order.
If it still does not work: check the invoicing software API key in Settings under “Company and taxes”. A failed invoice shows on the “Today” screen with the reason.