Hi Emby,
It's important that you're able to issue the refund payment to more than one credit. I'll be happy to assist you with this.
In order to match the refund with the credit, the two would have to have the same total amount. If they're different amounts you won't be able to match the transactions. Are your totals the same? Feel free to send screenshots. In the meantime, here's a helpful resource with more info on matching transactions.
Let me know if you have questions. I'm here to help.