Thanks for the question; I want to make sure we're on the same page here. You're processing payments through your website, which is connected to Intuit Merchant Services. When you try to refund through your website, it's showing declined on the QuickBooks side, is that correct?
If that's the case, you would want to reach out to the Payments support team. One of our representatives will be able to pull up your account and review why those transactions are declining.
Here's the contact information for Payments Support: