Credit Memos through iSupplier Portal

Hello,

We are on 12.2.3 and use iSupplier Portal.Some of our suppliers are entering credit memos through isuppiler portal by entering  a negative qty when creating the invoices and these are coming over fine into the AP module as credit memos.We wanted to know if this is a good process to allow suppliers to enter credit memos from isupplier portal or should they just submit regular invoices .Are there any problems if this is done?

thanks

rahul