Calling getLabels API operation

I used to be able to call the getLabels operation at /fba/inbound/v0/shipments/{shipmentId}/labels and retrieve Amazon LTL shipment labels (pallet + carton). This week when I tried to do the same Amazon is saying the CartonID value must be included in cartonIdList. If I didn’t save the CartonID value when creating the feed, does it mean I can’t retrieve the labels via API anymore?