Using external payments for games services such as PSN and XBOX pass

I would like to understand the restrictions that apple apply to apps that offer external payment methods for services that are not part of iOS app IAP system.

There are companies that sell vouchers for PSN, Steam and XBOX that are not related to IAP purchases, and are used in consoles external to the iOS environment.

But it seems that a payment app cannot offers such services inside iOS.

Could someone give me an explanation why is that so?

thanks in advacne,

Using external payments for games services such as PSN and XBOX pass
 
 
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