is the money in your account, i mean is the parking revenue credited to your account or in pending state? if it hasnt been credited and in your account balance you cant use it, it might take some time to get credited too.. you can check your account balance after you login here https://www.dynadot.com/account/ bottom of first box Account Info
You can only spend the money you have in your Account Balance. To renew a domain using that money, you'd process your order as normal, but when you get to the Payment page, you'd press the "Apply Balance" button.