I can understand your question whether it’s possible to start a mixed flavoured subscription, variation rocks! Fortunately, this is definitely possible and I will shortly explain how you can do so.
First, place 20 shakes of the preferred flavours in your cart. Make sure to tick the subscription box every time before adding a flavour to your cart, this means three times in total.
In your cart, you can then manually adjust the number of shakes for every flavour. The only thing to keep in mind is that the total amount of shakes in your cart should be 20, or a multiple of 20. This means that, for example, it is possible to monthly receive 7 vanilla, 7 forest fruit and 6 banana shakes. The price will be calculated based on the total amount of shakes in your cart.
I hope this information helps, let me know if you still have any questions!