Tks Saguaros for the quick reply!
There was no payment method. The issue is when using a promocode.
I added a user/student account (see Edit Fields) for you to use.
You can use the Promo code gurupro77 for anyone of the courses listed at https://globalsparks.com/index.php/microsoft-office/gurupcategs/49-microsoft-office/view
Note: in case this is relevant, although the error comes up, the confirmation emails go out to student and to admin stating that the registration is completed, but the students do not actually have access to the new course and it doesn't show up on their "My Courses" page.
Let me know if I can provide you with anything else in this regard.
Regards,
Serge