[Plugin: WP eCommerce] Purchase button not working

I am using WP eCommerce version 3.11.2 at https://kglrc.org/shop

When users add items to the cart, enter info and then hit <Purchase>, the button doesn’t take them anywhere. It just reloads the page.

I’m not sure what might be causing the issue, although we haven’t had a store purchase in quite some time, so it may not be a recent change.

Thank you!