We need to customize checkout process in VirtueMart. There are two categories of products in our shop. We need to customize checkout process so customer is not allowed to finish checkout before adding product from category 2. On the other side we may let customer finish checkout if he chooses to buy product alone from category 2.
So, no checkout from category 1 without product from category 2, but in same time customer must be able to checkout if select only product from category 2.