If your current balance is less than the amount you are trying to refund, can either initiate the refund once you receive further payments or you can add funds from the My Account section of your Dashboard.
You may refer to this short animation in order to add funds from your dashboard.
Please note, Add Funds works over your own account. Therefore, a TDR will be deducted on this as well. If you are adding funds for a large refund, you can send us a request: here