Measuring the success of Facebook Pay would depend on the specific goals and metrics set by the product team. However, some potential metrics to consider may include: 1. Adoption rate: The percentage of Facebook users who have signed up for and are actively using Facebook Pay. 2. Transaction volume: The total amount of money being transferred through Facebook Pay on a daily, weekly, or monthly basis. 3. Customer satisfaction: User feedback and ratings on the ease of use, security, and overall experience of using Facebook Pay. 4. Conversion rate: The percentage of users who have completed a transaction using Facebook Pay after initiating the payment process. 5. Retention rate: The percentage of users who continue to use Facebook Pay over time. 6. Cost savings: The amount of money saved by Facebook in transaction fees compared to other payment platforms. It is important for the product team to set clear and measurable goals for Facebook Pay and regularly track and analyze these metrics to determine the success of the product and identify areas for improvement.