Clause 3.1.1 in the App Store Review Guidelines states:
"If you want to unlock features or functionality within your app, (by way of example: subscriptions, in-game currencies, game levels, access to premium content, or unlocking a full version), you must use in-app purchase."
Once deployed, you will be able to collect payments via Apple's default in-app purchase feature, which enables Apple to collect payments on your behalf, in exchange for a percentage of your payments.