Hey I work at Braintree on our SDKs. You can find the list of things you need to do to enable one touch here[1]. For Android there is nothing outside a normal Braintree integration you need to do and for iOS you need to register a URL type as well as make two changes in your app delegate to tell us about it.

We generally think about two ways you can integrate with Braintree on the front-end: the drop-in UI and custom. Drop-in [2] means you yield control to us, but you get a dead simple integration which includes one touch paypal and venmo out of the box. If you go the custom[3] route it's obviously more work to integrate, but adding one touch only requires some button that starts the paypal or venmo flow.

Edit: You can also download ParkWhiz (https://itunes.apple.com/us/app/parkwhiz-find-book-parking/i...) and install the PayPal app to see the user experience for yourself!

[1] https://developers.braintreepayments.com/ios/guides/one-touc... [2] https://developers.braintreepayments.com/ios/sdk/client/drop... [3] https://developers.braintreepayments.com/ios/sdk/client/payp...