If you need to cancel a shipment and it has not been shipped yet by carrier, you could delete the shipment record created with A5 Ship app in Salesforce or the shipment status will remain “ready to ship” if you would like to keep the shipment record. It is only when you give the package to the carrier to be shipped that the carrier will scan and process the label so if they have not yet received package, you can “cancel” the label before shipment starts.

If the shipment has been shipped or in route to destination, you will need to contact the carrier directly to cancel the shipment.