Refund

This API will allow to process a full or partial refund for a paid or partially paid transaction.
To process a full refund just specify the invoice ID, to process a partial refund add the amount of the refund.
Multiple partial refunds for the same invoice are allowed until there is "credit" in the invoice.

If the refund amount exceeds the invoice credit an error message will be display and te refund will not be processed.
Refunds are only available for invoice that have a successful credit/debit card transaction.
Direct debit refunds are not available.