What is the required permission for displaying push notifications on iOS?

The required permission for displaying push notifications on iOS is to request authorization from the user via UNUserNotificationCenter. This process involves explicitly asking the user for their consent to receive notifications. When an app wishes to send push notifications, it must first present a prompt to the user, using the UNUserNotificationCenter's method to request authorization. This ensures that users are in control of their notification settings and can opt in or out as they see fit.

When an app requests permission, the user can choose among different options: allowing notifications, allowing notifications with alerts and sounds, or denying notifications altogether. This explicit consent process is designed to respect user privacy and preferences, aligning with Apple's guidelines on user data and notification handling.

The other options do not align with the iOS notification permission requirements. Automatically enabling notifications upon installation would violate user autonomy, as consent must be obtained first. Using a specific server key for notification access does not pertain to user permissions, as server keys are utilized for backend communication rather than user consent. Similarly, requesting a user email for notification opt-in does not relate to push notifications; email and push notifications are two separate channels of communication.