I have the same issue and I still haven't found a solution too

I encountered the same error in iOS 18.2(22C5142a).

same error in iOS 18.2(22C150).

I solved the problem. Systems above iOS 18.2 need to call the purchase(confirmIn:options:) interface and pass a confirmIn parameter. See https://developer.apple.com/documentation/storekit/product/purchase(options:)#Discussion