From the Payments tab in the BitPay merchant dashboard, use the filter option in order to locate the invoice for which you have a pending refund request (use the BitPay invoice ID as filter option). Click on the corresponding payment entry to access the payment details
A message on top will indicate if there is a pending refund request for the selected BitPay invoice. Scroll down to the bottom of the page to display the transaction history for this BitPay invoice.
Click on the inverted arrow button next to the "refund Pending" entry. This will display the Cancel button which allows you to cancel the pending refund request.