As the product manager for WhatsApp with $1B of investment, there are several areas that I would focus on to improve the product and grow the business. Firstly, I would invest in improving the user experience of the app. This would involve conducting user research to identify pain points and areas for improvement, and working closely with the design and engineering teams to implement changes that would enhance the usability and functionality of the app. For example, I might explore ways to make it easier for users to find and connect with their contacts, or to share multimedia content like photos and videos. Secondly, I would work on expanding the reach of the app to new markets and user segments. This would involve developing a deep understanding of the needs and preferences of users in different regions and demographics, and tailoring the product to meet those needs. For example, I might explore ways to make the app more accessible to users with low-end devices or limited internet connectivity, or to offer features that are particularly popular in certain regions. Thirdly, I would focus on monetizing the app in a way that is sustainable and aligns with the values of the company. This might involve exploring new revenue models, such as offering premium features or targeted advertising, or partnering with other companies to offer complementary services. However, it would be important to ensure that any monetization strategies do not compromise the user experience or compromise the privacy and security of users' data. Overall, as the product manager for WhatsApp with $1B of investment, my goal would be to build a product that is loved by users around the world, while also delivering long-term value to the company and its stakeholders.