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The Billing Address that is required to be filled out in your Pro Checkout/Membership # Level Forms is generated automatically by s2Member, and is not stored on your site by s2Member at any point.
If you’d like to have access to your user’s address, you’ll need to create Custom Registration/Profile Fields, and have your users fill out both the Billing Address associated with their credit card, and an address that will be used on your site.
There is currently no way to get a user’s Billing Address through these forms directly. Custom Registration/Profile Fields have to be made to accomplish this.
If you are looking for a way to populate your Custom Registration/Profile Fields based on the user’s Billing Address, s2Member’s CSS Styles and Other Attributes sections of the Create/Edit Custom Registration/Profile Field screen can help accomplish this.
See: Dashboard -› s2Member® -› General Options -› Registration/Profile Fields
You may also need to edit the standard s2Member Pro Form checkout template to accomplish this. If you are uncomfortable editing these template files yourself, you may want to hire a freelance developer to help you. We recommend http://elance.com/ and http://jobs.wordpress.net/ for finding developers familiar with WordPress/s2Member.
See: Is it possible to modify s2Member® Pro Form templates?
See Also: Video » s2Member (Custom Fields Dynamically?)