Not long ago, riders on buses and trains across the world paid their fares with tokens. Eventually, tokens were replaced by sophisticated electronic swipe and tap cards and tickets, which are the primary fare media today. Several agencies now use mobile apps to collect fares. However, public transit services in most metropolitan areas in the United States are highly fragmented among multiple modes and providers with various methods of payment. Integrating fare payments systems provides riders with smoother transfers. With private mobility services like transportation network companies (TNC) playing a significant role in many journeys, the landscape of payment systems is growing more complex.