What is one real world example of a regulation put in place to eliminate an externalized cost? What externalized cost was targeted by this regulation?

when externalized costs are internalized, the total cost is less. Why do the costs decrease?

How does PayPal benefit from this program? How does society benefit? Be specific. For example, do not say PayPal makes more money. Instead, explain how PayPal makes more money directly as a result of this program?