The Cart is deprecated
While you can still use the Cart, it's no longer being developed. For the next-gen, easy to use, way of integrating Two Tap contact us at firstname.lastname@example.org.
The Cart HTML5 interface is a pre-created checkout interface on top of our API. It is white-label and designed as mobile-first.
To use it just point a web browser, a UIWebView (iOS), or a WebView (Android) to https://checkout.twotap.com with a pre-created checkout_request.
The Cart interface is stateless, which means you can't add products to an existing cart. For multi-products / multi-retailers we recommend you store the list of product URLs locally (localstorage, NSUserDefaults), and open the interface once the user taps your checkout button. You don't have to do any extra UI work since you would have a 'checkout' button (that contains a count of products in the cart) anyways. When shoppers press that button open Two Tap with that array of product URLs.