Stripe not loading


We have set up a course press site-

We have set up a course which has a cost.

During sign up to the course, it clearly attempts to load stripe- our chosen payment gateway, but fails- it gives a blank lightbox - see attached.

Any ideas what is going on? I'm not sure if this is an issue with the payment gateway set up or the course press/marketpress trying to call the screen?

I have updated the plugin to the latest version and wordpress to the latest version.