The listing on the directory is a one off payment that allows your company to be listed for a year. The billing is recurring and your credit card will be charged once every year on the anniversary of the date you joined. You will receive an email to warn that you are about to be billed and you can stop the cycle at any time by logging into the site and changing your Account settings (top right of every page).
Payment is via Stripe a well established and secure payment system/gateway, this system will also allow you to pay via a company Amex card for no additional fee.
If you have any questions please contact the membership team firstname.lastname@example.org