There are a number of reasons why you might be experiencing an issue where you cannot select the flavour or size of an item. It generally comes down to whether the item is in stock or not.
When a product is out of stock, the website automatically takes away the options of choosing flavours, sizes and the ability to add it to your cart. While it may not say out of stock anywhere, it won't allow you to change any of the variables or add it to your cart.
If it is a bundle that you're looking at then unfortunately package deals can only be purchased with items that are in stock. If you select a bundle deal and one item is unavailable, then the whole deal is unavailable.
For more information regarding items out of stock or alternative products please Call Us on 1800 443 637 or contact us via Live Chat.