Which of the following is NOT a standard event defined by Meta?

The choice of "Subscribe to newsletter" as the answer is accurate because it is not categorized as a standard event defined by Meta for tracking user interactions. Standard events in Meta's framework are predefined actions that can be used to measure conversions and user engagement effectively across platforms, such as "Add payment info," "Complete registration," and "Initiate checkout." These events are crucial for e-commerce platforms and are specifically tailored to facilitate robust tracking and optimization of ad campaigns.

On the other hand, while subscribing to a newsletter is a valuable action for businesses, it does not fall under the commonly recognized standard events that Meta defines for measuring commerce-related activities. This distinction highlights how businesses might track specific goals that are more aligned with customer acquisition and lead generation outside of the customary purchasing funnel that the other choices represent.