Having received my tiles from the Black Friday bundle, I decided to get some more for Christmas gifts, after receiving an email about ongoing sale prices.
While playing my order, I entered MPU for the discount code and got free shipping.
However, there is a bug on the website that isn’t allowing me to complete the purchase. 
Gotta call support tomorrow morning.
The moral of the story is: Always enter MPU for the discount code, even if you don’t know that it’s valid!