How to Record a Refund Event?

Hello,

I have a scenario and I would like some advice / help.

Say I raised an Invoice of $1000 to the customer for some services which I want to offer him. The customer pays and I mark the invoice as paid (add payment).

Then one fine day customer is not happy and request for a refund. We have already given him services worth of $400, so now we have to refund him the balance $600. So, how do we record this event? Ultimately, at the end of the transaction, we have only made $400 and all accounts with this customer are closed and nothing is due to anyone.

I just need to make sure these events can be recorded properly so in future if we want to know what happened, we have proper records. Please help.

Cheers,
Shaf