Calculate the total payment of orders for Vegie-spread product.
Vegie-spread product refers to ProductName = 'Vegie-spread'；total payment = MULTIPLY(UnitPrice, Quantity, (1-Discount))
SELECT SUM(T2.UnitPrice * T2.Quantity * (1 - T2.Discount)) AS sum FROM Products AS T1 INNER JOIN `Order Details` AS T2 ON T1.ProductID = T2.ProductID WHERE T1.ProductName = 'Vegie-spread'