Checkout Buttons need to be pressed twice

Hi,
I have just set up my eshop plugin and have set it up with a product.

Once i have the item in the cart and have entered my information, I press the “Proceed to confirmation” button and the loading circle comes on but the page does not change. Only when I press the same button again does it go to the next page (Checkout – Please Confirm Your Details). The same thing happens on this page when I try to press the Proceed to checkout button.
Here is the live link for the product:
https://www.pumapix.com/2015-calendar/

Any advice on how to make this a single click? Most customers would be afraid to press the button twice.

Thanks so much!
Sebastian

https://www.ads-software.com/plugins/eshop/