Every time a consignment is submitted it creates a Message Request to the API of the Shipping Agent. You can view the Message Requests associated with a Consignment by selecting Navigate, Message Requests.
The Message Request are displayed with the most recent at the top. Submissions that produced an error are displayed in red. There should only be one successful submission (i.e. displayed in black) per Consignment.
By selecting the line with an Error Status then selecting Navigate, Error Log you will be able to see the error message returned by the shipping agent API.