If you have created an Account Credit, and want to refund it to a credit card, you'll have to use a reference transaction from the original invoice.
Go to the original invoice and copy the transaction ID associated to the credit card you want to use.
Then go to the newly created invoice and paste the transaction ID in the "Create Reference Transaction" Box
Enter the negative amount you are crediting back to the customer along with a payment note if desired. See below example of how the last step will appear.
You can create a reference transaction from any transaction ID but the invoice that the refund payment will get added to will be the one you are currently on when processing.
If you have multiple locations with different CardConnect accounts attached, your reference transaction must be in the same location the original transaction took place. You will receive an error if you try to submit a transaction to a different location's CardConnect account.