def refund!(opts)
      opts = opts.merge(:sale_id => self.sale_id)
      Twocheckout::API.request(:post, 'sales/refund_invoice', opts)
    end
def refund!(opts)
      opts = opts.merge(:sale_id => self.sale_id)
      Twocheckout::API.request(:post, 'sales/refund_invoice', opts)
    end
Refund sale