I see you have problems on a real device too but I bumped into the same issue but only for Simulators and I've found out that RevenueCat has the problem with the iOS 18.4, 18.4.1, and 18.5 simulators.

The workarounds are:

1 - Test on Physical Device​

2 - Use StoreKit Configuration Files​

Create a StoreKit Configuration file in Xcode. Use local testing instead of App Store Connect sandbox. Configure your products directly in the configuration file

3 - Use iOS 18.3 Simulator

Their issue described:

https://www.revenuecat.com/docs/known-store-issues/storekit/ios-18-4-simulator-fails-to-load-products?utm_source=chatgpt.com