Access to FulfillmentOutboundShipment.CreateFulfillmentOrder is denied Documentation
Typically, this means you might be trying to connect to the wrong server for your region or your MWS credentials are not correct. Confirm your WooCommerce Amazon Fulfillment settings for the connection between Amazon and WooCommerce under Setup and Configuration. Ensure that your region is correct in the dropdown. Note: UK marketplace belongs to the EU region.