I want to make sure you get the answers you need with the error message you're getting when processing credit card refunds.
Our Support Team has not communicated any reported issues from other users about the problem with the Merchant Services Center. While there isn't any investigation created for this, I'd suggest getting in touch with our Merchant Support Team.
There they can check your account and provide you additional workarounds to help you process your customer refunds successfully. Here's how you can contact us: QuickBooks Payments
Please keep me posted with the outcome, Geri. I'm here to lend you a hand whenever you needed help.