What is the difference between using Paypal and In-App Purchase?

What is the difference between using Paypal to pay the money and using In-App Purchase for payment?

I want to do booking of any event tickets and payment of that from iPhone. Either us开发者_StackOverflow社区ing Paypal or In-App Purchase.

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As was mentioned in a comment above : https://developer.apple.com/appstore/resources/approval/guidelines.html#purchasing-currencies

The apple purchasing guidelines are your best bet for understanding what IAP can/cannot be used for. In general IAP is designed for purchasing digital goods for use on the purchasing device. If you wish to sell services/goods IAP is expressly forbidden for this purpose and you MUST go outside the bounds of IAP. Paypal is a great resource for this because it's a very commonly used payment mechanism and they have SDK's for iOS that are fairly easy to implement.

I would suggest reading the above link that @Luke posted as well as the paypal MPL sdk documentation. However if you are also going to have a website where you have a paypal cart built as well paypal has other libraries that you may find useful. (don't get overwhelmed by the # of options https://www.x.com/developers/paypal)