Can i use Paypal payment in my app to sell digital photographies to our customers ?

I've use paypal and cach payment in my application to allow to our costum to buy there photos , but the apple team had reject my app by mention this info

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Guideline 3.1.1 - Business - Payments - In-App Purchase

We noticed that your app or its metadata enables the purchase of content, services, or functionality in the app by means other than the in-app purchase API, which is not appropriate for the App Store.

Specifically, your app allows the purchase of digital photographies via PayPal or Cash payment.

Next Steps

While the payment system that you have included may conduct the transaction outside of the app, if the purchasable content, functionality, or services are intended to be used in the app, they must be purchased using in-app purchase, within the app - unless it is of the type referenced in guideline 3.1.3 of the App Store Review Guidelines.

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Thanks for help