I have several large suppliers that offer discounts / credits for early payment. I need to be able to apply these credits to the invoices and have them appear on the Remittance Advice as a credit note, but can't seem to find how to do that:

I have found something which refers to a remittance advice credit refunds - but can't find how these get generated through this system as this would potentially resolve my issues as well.
Thanks in advance.
Tanya