In-App purchases are for digital goods only (Content, Functionality, Services, Subscriptions). You are completely free to sell real/physical goods (ie. a train ticket) via your own payment system.
It amazes me how many people continue to misunderstand App Store rules and quote bullshit on a daily basis.
In-App Purchasing rules apply to purchasing books in an e-reader, levels in a video game, or music in a player, etc.
It doesn't apply at all to real-world items. (This includes something like train tickets via Passbook because they are not consumed in the app, they are consumed by the train conductor scanning your phone.)
https://developer.apple.com/appstore/in-app-purchase/In-App-...
"You must deliver your digital good or service within your app. Do not use In-App Purchase to sell real-world goods and services."