With fast development of mobile devices and respective software collection of in-app payments becomes an extremely relevant issue for many businesses. Development of mobile POS systems (MPOS systems) and handling of in-app purchases represent important aspects within the activity of companies that operate online and have to handle card-not-present payments.
If you want to be able to accept mobile payments, you can follow one of several approaches. The first and the easiest route to take is use an online app marketplace. In this case the app marketplace owner handles payments made through your apps, using one and the same technology for selling the apps and for accepting payments within these apps. The second approach is to use some third-party wallet or payment page, to which the user is redirected when he makes a purchase. The third option is to integrate with a third-party payment gateway. Finally, the fourth option is to use alternative methods for accepting in-app payments, such as ApplePay or AndroidPay.
Before selecting one of the listed options you need to decide how much you are willing to pay, how much control of payment information you need, whether you need to store cardholder data (or respective tokens) for recurring billing, whether you are ready to go through PCI audit, and whether you need to store information for recurring billing.
An article, describing the pros and cons of different in-app payment handling methods is available on Paylosophy.