Pop-up notifications are often annoying. For Meta, one in Apple's iOS operating system, which powers iPhones, is a particular headache. On February 2nd Meta, which owns Facebook and Instagram, told investors that privacy-focused changes to iOS, including the "ask app not to track" notification, would cost the company around $10 billion in 2022. That revelation, along with growing competition and sluggish growth in user numbers, helped to prompt a 23% plunge in Meta's share price and showed Apple's might. But what did Apple actually do, and why was it so costly?