Error: You must include a valid ShipmentId with a call to the CreateInboundShipment operation. Get ShipmentId values by calling the CreateInboundShipmentPlan operation. The request to CreateInboundShipment must include only items and quantities that have been previously planned through CreateInboundShipmentPlan. If a ShipmentId is not used to create a shipment within 48 hours it will expire.  

This error happens when the shipping plan has expired, typically when it is older than 48 hours. To refresh the shipping plan, hold down the Shift key and click Create Shipment / Regenerate Shipment Plan.