There are some things that you'll have to keep in mind when creating a new shipment for your POs:
Concept
Too Keep In Mind
Ship date
If the setting on the vendor options tab is enabled, make sure that the AWB ship date matches the ship date of your POs, if they don't, the system will not let you add the items to that shipment.
Confirm POs
Only confirmed POs can be added to an AWB; otherwise, vendors won't be able to see them on the Pending Orders window.
AWB status
Users can make any change on the AWB as long as it's open. The system will automatically close the AWB two days after the ship date to prevent any alterations.
Reprint labels
Whenever a change is made, all labels have to be printed again.