How to Refund Transactions in macOS
To refund a transaction in macOS, right click it and select "Refund" from the menu. You can also use the hot key for this action: ⌘ + R.
How to Refund Transactions in iOS
To refund a transaction in iOS, tap a transaction and select "Refund".
Things to Consider
You should not change the category when creating a refund in order for the refund to be properly recorded into the original category. You can change the amount in case of a partial refund.
You can delete some of the categories when creating a refund for a transaction that includes multiple (split) categories.
Please note that only a single transaction can be refunded at once.