My card seems to have been charged multiple times.
If you had trouble submitting a payment form and it now seems as if your card was charged more than once, please read on.
Each time a user attempts to submit a payment form, our payment processor–Stripe–asks the user's credit card company or bank to authorize the payment. If everything on the payment form is correct and complete, the form goes through, the payment is "captured", the user is redirected to a page confirming payment, and a receipt is sent to the user by email right away. If you got a receipt, we got the payment.
However, if the payment form is incomplete or there is a problem with it, the payment authorization remains "uncaptured" and it is automatically cancelled after a period of 1-2 hours. No confirmation page is served and no receipt is emailed. A subsequent check (give it at least two hours) with your bank or credit card issuer should show that any incomplete payments were cancelled.
Unfortunately, we have no control over how that all works with Stripe and the credit card issuers. We would fix it if we could.