Proceed to Checkout Issue

Hi there,

When I add the product to the basket it goes in fine, but when I view the basket..
https://transitionsack.com/cart/

I can’t Proceed to Checkout for some reason. It was working fine but then stopped working. I can see the checkout page fine when I preview it from the page preview, it just won’t work when trying to link using the button in the basket for some reason. Even if you put the cart url in it just goes to step 1 of the order process.
It should obviously re-direct to this url.
https://transitionsack.com/checkout/

The page I need help with: [log in to see the link]