GoMarina lets you easily pay port fee and other products and services in guest harbors.
Registration is easily done with a one-time password via SMS. After registering you can add info and a photo of your boat, so that your purchases are associated with your boat.
Payment is done with credit cards. You only have to enter your credit card information once, later charges will be made through the same card. Information is never stored with us, but with the payment provider, according to their guidelines for privacy and security.