iOS provides a comprehensive set of SDKs and APIs to build great applications. However, a successful app needs to be integrated with many different third-party services to deliver the best services and experience to the end-user. To make iOS apps more versatile, we integrate apps we develop with many other external systems., PayPal, Stripe are a few of the payment gateways we frequently integrate with apps we develop. For push notifications, we use external services such as Firebase and Urban Airship. These services provide more reliable, manageable and scalable solutions to scale the apps as required.