From the Transaction history you can Void the last approved transaction.

Note: Processing a Void will stop a transaction from being charged. Funds will be returned to the customer's card within 1 – 3 business days. You can only Void the last transaction.

1. Select History from the navigation bar.
2. Select the last approved transaction.
3. Select Void on the transaction summary page.
4. Press Confirm.
5. A confirmation screen will appear confirming if the Void was successful. A digital receipt will be available for the customer.

‍