post https://{environment}.{server}.com/v3/transaction/
A refund should be used once the transaction you are refunding has settled. If you are trying to cancel a transaction that is still in the currently open batch, you should use the void command instead.
To refund a transaction that has been settled, you will pass in the transaction object with the type of 'refund', the original transaction id, and the amount you would like to refund. Most merchant accounts do not allow you to refund more than the original amount of the transaction. However, depending on the Credit Policy, a refund can be processed for larger than the original transaction amount.