As noted in the title, I want to buy the 5e Cthulhu Mythos book, but every time, it is written in the cart that “Your cart contains items that cannot be shipped from our current warehouses.”

I don’t understand what can be causing this issue, since I had no problem to subscribe to the Big Sleep adventures… Am I the only one with this problem? As a side note, I reside in Canada. Might this be the issue? And if yes, is there another way to get the book?