The purchase price of a product usually changes during time, WAMA supports different purchase prices for the same product.
The purchase price is associated to a positive stock change. When you create a product with quantity zero no purchase price can be associated to the product as nothing has been purchased.
The purchase price can be defined at two different times:
The purchase prices of each positive change of the product quantity is saved in the positive product history entries. In order to change a purchase price for an old stock change open the
product details and select the
History tab, here select the positive quantity to be changed, open it in edit mode and change the purchase price.