That sounds like an awful user experience. There's no way I'm ever buying a mobile app that requires me to go enter my credit card into a website to pay for it. Cross-platform services can justify this sort of thing (because you're buying a subscription to the service across all platforms), but doing it for what otherwise would be a paid app purchase is incredibly user-hostile.
I think you’re in the minority there - users enter their information constantly for physical items. Nobody raises an eyebrow, let alone calls it hostile.
Also, problem solved, just use Apple Pay on the checkout page. Ironic, but royalty free, and one-click to enable in Stripe.
