Can I use the Portal to find out why my invoices were rejected ?

In the list of invoices, the status indicates the initial reason for rejection: eInv rejected, Clearance rejected, etc.

The status tooltip gives you more details of the reason for rejection.

You can show the cause of rejection in the list of invoices issued by adding the “Reason for rejection” column. 

You will also receive the reason for rejection in your “Non-Compliant Invoice" email