Proteon does not actually perform the financial transaction for the chapter.  The website does set up the transaction and collect information but the actual transaction is facilitated by your payment gateway provider (Authorize.net or PayPal) so that is the system where the refund processing should happen.  You can log into itt and essentially 'reverse' a transaction.
 
We purposely do not link the website to the payment engine like other vendors.  They like to run your money through their systems so they can make interest off the float and they also can charge an additional 3% per transaction for their 'service'.  We avoid that by separating the systems.  Your money never gets confused with Proteon's money and it immediately goes strait into your accounts.  It is a simpler setup and has much more financial integrity.  The only downside is that you need to log into the payment geteway to perform a refund.