Refund a settled transaction. If you are trying to cancel a transaction that is still in the currently open batch, you should use the void command instead. There are two kinds of transactions that can be refunded:

Credit Card Transactions

Performed by passing the transaction object with a type of 'refund' and the amount you would like to refund. Depending on the Credit Policy, a refund can be processed for larger than the original transaction amount.

ACH Transactions

Performed by passing the transaction object with a type of 'refund' and the amount you would like to refund. The amount cannot exceed the original transaction amount.