If you find that you're unable to proceed to the checkout page, it means at least one of the products in your cart has just gone out of stock before you were able to finish your order. This is a rare instance as it means someone else has placed an order for the same item at the same time as you but was able to complete their order before you. You will need to remove that item from your cart and then proceed to checkout the order. We apologize for the inconvenience, you can contact us for further help if you experience any further issues.