How to handle external purchases on iOS 15.4 - 17.3 without StoreKit modal?

Hello everyone,

I’m implementing external purchases in my app and I’m using ExternalPurchase.linkToExternalPurchase() on iOS 17.4+ to display the Apple modal for external purchases. However, I need to handle purchases on iOS 15.4 - 17.3, where StoreKit’s external purchase APIs do not provide tokens and return false.

Questions:

1. What is the recommended fallback for iOS 15.4 - 17.3 since the Apple modal is not available?
2. Should I display a custom modal or directly open a WebView with the purchase page?
3. On iOS < 15.4, since external purchase APIs are unavailable, is it acceptable to open the external purchase page directly in Safari instead of within the app?
4. Will Apple reject the app if I use a custom modal for purchases on iOS 15.4 - 17.3 instead of the Apple-provided one on iOS 17.4+?

I want to make sure my implementation complies with Apple’s guidelines while providing the best experience for users on older iOS versions.

Thanks in advance for your help!