Enter coupon code exactly how it appears and click apply. Once applied it will not ask for any of your card information except your name.
If you're using a coupon, a message will appear here saying "The credit card field will initiate once the payment condition is met". That means it's working, next just type in the card holder name and submit. Also if you're using a coupon, email firstname.lastname@example.org when you are finished so your account can be activated.
Please check if you have activated a Stripe feed for your form.