The Purchase credit not is used in case you want to return of goods to your supplier. They are also used in cases where the vendor, for whatever reason, offers you a discount on already invoiced items.
To add the credit notes issued by your suppliers at Elorus, select Invoicing -> Purchase credit notes -> Add.
As with sales credit notes, you can correlate the purchase invoice with the credit note from the "Related Documents" field, regardless of whether it is paid or not.
Attention: In order for the supplier's balance to be correct after a refund, the value of the credit note must be used to pay off the purchase invoice. This can be done by adding a payment either from the sales document view page or from the credit note's page using "Apply credit".