Solved this problem on my project. Updated my deprecated code to StoreKit 2. As I've been using UIKit, I needed to call purchase(confirmIn:options:) function. https://developer.apple.com/documentation/storekit/product/purchase%28options:%29#Discussion

Solved my problem using the call @zbjumper shared. Call purchase(confirmIn:options:) on UIKit projects

Since iOS 18.0, I've encountered lots of StoreKit deprecated code on my projects, I recommend to set Minimum Deployment to iOS 18.0 and update any StoreKit deprecated code or upgrade everything to StoreKit 2

Are you using Storekit 1 or Storekit 2? I'm using Storekit 1 and in-app purchases are not working on iOS 18.2

Clicking 4 times on "Save" worked for me, can't believe 2 years later and they haven't fixed this bug.

Here you can do it:https://developer.apple.com/programs/enroll/