For extra fraud protection, some banks require customers to complete an additional verification step. You may be asked to enter a password associated with your card or a code might be sent to your phone, depending on what your bank uses for card authentication, and might look something like the screenshot below:
Some banks only require this authentication for the first charge, while others may require it on a monthly basis. In these cases, an email will be sent to you around the date that your subscription is due with a reminder to authenticate the charge once again.
If you experience any issues with authentication, you will first want to contact your bank/card issue to ensure the charge is approved on their end before contacting iWin Support.