Unable to Checkout using firstdata, cannot proceed

We recently bought a Hikashop Starter version to integrate a very simple shopping cart. Everything works as expected except on the checkout page. The one and only method to checkout is credit card (firstdata). The plugin has been setup correctly, we double checked that. When I fill in the credit card details and hit next, the page refreshes but nothing else happens. I am on the same page again and cannot proceed with the checkout. There is no error message, nothing.

This is for a client's website that must be launched asap.