The IAP Unity Guide (Unity - Manual: Configuring for Apple App Store and Mac App Store) leaves one vital part out.
When you add your IAP to the iOS App Store via App Store connect, the Unity Guide does not tell you to add a localization name and description.
If you don’t add a localization name and description your product name and description for the IAP will be invisible in the UI. So do make sure to add it as pictured below:
