I have tried printing a FedEx shipping label and am seeing an error returned:
CommercialInvoice FreightCharges - Invalid currency
InternationalDetail CustomsValue - Invalid currency
UnitPrice - Invalid currency in Commodity 1 (COMMODITY_INDEX=1)
CustomsValue - Invalid currency
Please review the currency on the order and make sure that is correct. Currency can be changed if you edit the order in Open Orders screen. Additionally please verify that the destination country has the correct currency set in Linnworks.net > Settings > Countries.