We recently designed eliquidparadise.co.uk; and they have created multiple categories of products. Using attributes and variables, we have managed to configure the "3 for 1" price in individual products, for example here; https://eliquidparadise.co.uk/product/american-lites/
However, we want that people can add several items to their basket, and that a "3 for 1" offer works in their basket if they buy different products and / or different categories.
3 different flavors
2 articles of the Prestige category and 1 article of the Vjuice category.
Both previous examples we would like to qualify for "3 for 1" at fixed and discounted prices.
Please advise, all the answers are very appreciated.