An In-App Billing developer designs and implements in-app purchasing strategies within a software application. They integrate APIs for various payment systems to facilitate transactions, ensuring a seamless user experience. Their work involves maintaining secure, efficient, and effective in-app purchase systems. They also handle troubleshooting, updates, and improvements to these systems. Their role is crucial in monetizing apps, offering paid features or digital products. They need to understand various payment systems, platforms, and regulations. Moreover, they work with other developers and stakeholders to ensure the in-app billing system aligns with the overall app design and business goals.