In order to address the merchants' concerns about adding friction and hurting conversion by requiring billing details in Stripe Checkout, I would approach the problem by conducting user research. I would aim to understand the needs and pain points of both the merchants and the customers in the checkout process. This research would involve both qualitative and quantitative methods, such as surveys, user interviews, and A/B testing. Based on the insights gathered from the research, I would then work with the design and engineering teams to come up with potential solutions. For example, we could consider providing more information to customers about why billing details are required, or offering alternative payment methods that do not require as much information. We might also consider making the billing information fields optional, while still providing incentives or reminders to encourage customers to fill them out. To ensure that any changes we make are effective, we would need to monitor the impact of those changes on conversion rates and other relevant metrics. We could use tools such as analytics dashboards and funnel visualization to track user behavior and identify areas for improvement. Overall, the goal would be to balance the needs of the merchants and the customers, while still ensuring that the checkout process is as smooth and frictionless as possible. By working closely with the teams involved and using data-driven insights, we can make informed decisions that improve the overall user experience and drive business results for Stripe.