Before any customer can be added to a Payment Stream, they must have the billing address filled in and have a payment method entered on their customer card. This can be done 2 different ways.

1. When you add them in manually, they can provide the payment information to you to be entered into their record.
2. You can send them an email with a link so they can sign into the secure customer site and add/update the information themselves.  (Refer to the ‘Create Customer Login‘ article)