I have been able to create a credit note using the API and have the Invoice# field filled in, however I am still able to create an extra credit note for the same item from the original invoice.

I want to be able to create a credit note on an invoice that cancels the original product from the sales order. As when you manually create a credit note from the invoice the Item gets cancelled from the original sales order and you can no longer create a duplicate credit note.

many thanks fro any advise :)