Assuming that the refund is not for the full amount of the invoice. You can do the following:

Step 1 – Open the Membership record

Step 2 – Go to the contact record and click “Add New Credit” and add the amount to be credited

Step 3 – Open the Credit on the record and do Refund Credit .  The screen should refresh and the credit note should be marked as “Refunded”

Step 4 – Process the refund by CC either through World Pay, Serve base or Bank transfer.

Step 5 – Put notes on record to say what has been done