Ability of the supplier to cancel invoices in iSupplier portal ?

Hello,

How can a Supplier cancel an invoice for a fully invoiced Purchase order.

Let me explain with an example.

Say PO 123 is for 100 USD and iSupplier is set up in such a way that over invoicing is not allowed. That is a supplier cannot invoice more than 100 for this PO and we only allow PO invoices through iSupplier portal.No Non PO invoices via iSupplier portal.

Now,

A supplier fully invoiced for 100 USD for the PO 123.

He did a mistake he should have invoiced for only 90, however by mistake he invoiced for the full amount.

Now, to correct this situation is the Credit memo only option ? If there are any other options without the intervention of Account Payables team, please let me know.