3790770 - Why am I unable to add taxes, charges, or discounts to imported cXML invoices?

Why users are not able to add Taxes, Charges and Discount on the Invoice User Interface(UI) in Ariba Buying and Invoicing (B&I) for the invoices imported through cXML but working fine for the normal invoice. 
Why Add Item Details button fields on the Invoice is Greyed out?
Why users are not able to Edit the Invoice and not able to add Non-Catalog and Catalog item on the Add Item button for the invoices imported through cXML.

An Non-PO Invoice imported via Postman tool(External system) to Ariba B&I and also we can see that the invoice is stuck in ‘Submitted with Error’ status. 
When we try to edit the invoice system does not allow to edit/add the tax details or add a non catalog item options are greyed out. 

Taxes, Charges, Discount, Add Item, Imported cXML Invoice, Edit Invoice. , KBA , BNS-ARI-INV , Invoicing , Problem