Thank you for your patience here.
The difference is more or less if you decide what happens and if the amount has already been transferred to your account.
If the money has already been transferred to your account, you will have to refund / make a "GUTSCHRIFT" as you are technically paying the money back to the merchant. If the money has yet to be transfered (for example if this is a banktransfer order that has been placed incorrectly) - you can void / make a "AUSBUCHUNG" effectively cancelling the order and derecognizing it.
The same is the case for creditcard payments. If you only authorise payments / capture them manually in a second step, you can still void them / derecognize the order. This is the case because the amount has then only been reserved / not immediately claimed.
If the payment is already captured / captured directly, the credit has already been given to you and the amount has to be refunded.
I hope this explains the difference between these two.
If you have any further questions on this, please let us know.