You can read the full documentation here.
Our Mobile SDKs (Checkout) are client-side iOS and Android frameworks that handle customer credit card input within the merchant's app. This iOS framework limits the scope of a merchant's PCI compliance by removing the need for them to pass the sensitive information (credit card number, CVD, or expiry) through their servers and from having to write and store code that comes in contact with that sensitive information.
By integrating Checkout a developer can easily provide a way for users to accept payments in an iOS app. Checkout provides some client-side validation, smart field data formatting and a design that works in all iOS device form factors.