Which step is essential for ensuring a user can set up cardless purchases securely?

Specifying a secure email address is crucial for facilitating cardless purchases securely. A secure email address serves as a primary point of contact for authentication and communication between the user and the service provider. It helps verify the identity of the user during the setup process and is often used for sending one-time passwords, transaction alerts, and account confirmations.

Using a secure email address enhances security by reducing the risk of unauthorized access. If a user has a compromised email account, this could lead to vulnerabilities in the cardless purchasing process, such as identity theft or fraud. Therefore, ensuring that the user provides an email address that is not only secure but also one that they can access is a fundamental step in establishing a secure online purchasing environment.

The other choices, while potentially relevant in different contexts, do not address the specific aspect of secure user identification and authentication necessary for setting up cardless purchases.