How to refund extension

One opencart user bought an extension from me (through opencart extensions site).
However, the extension didn't fit him because he want it to be on a custom page.

Now he asked me if i am able to fix it and i said i would take a look. However, it looks pretty hard and i don't know for sure if i am able to do it right.

My question is:

He didn't ask for a refund, but if he did, or I wanted to give him a refund because the extension didn't fit him, How can I refund the $10 he paid?
I can't do it through my own paypal because Opencart is getting 30%.

So how do I refund? Is it even possible ?

greetings

Hi,

You can just tell him to request for a refund here
http://www.opencart.com/index.php?route=support/contact

there's a "I want to get a refund" option

Cheers,