Refund vs void
When you're viewing the details of a transaction you see two options. You can either Refund it or Void it.
REFUND: This will be selected if the original transaction took place 24+ hours in the past. For example, if a registrant signed up or made a donation yesterday or sometime in the past, I can click on the Refund button and issue a partial or full refund. Some gateways do not require full credit card details to issue the refund. Just the amount you wish to refund. Other gateways do.
VOID: A void is to be used if the original transaction occurred the same business day you are trying to issue the refund. For example, if a registrant signed up today and I am trying to issue a refund, there technically aren't any funds to refund because they have not yet deposited into my bank account. In this case, simply choose Void and it will prevent the transaction from ever processing.
CREDIT VOL EXCEEDED 0.0000
If a refund is ever attempted and the "CREDIT VOL EXCEEDED 0.000" is received, this is likely because the original transaction occurred today. Sometimes it can be due to the fact that the credit card was cancelled, or maybe it happened too far in the past and it might need to be issued through your virtual terminal.
*Partial Refund: You must wait until the transaction has fully settled in order issue a partial refund.