Ionic 3 app: Promocodes for in-app purchases not working

I published a new version of my Ionic 3 app three days ago with a new, non-consumable in-app purchase. I supplied some iOS users with promocodes from App Store Connect to get this in-app purchase for free. But these codes are not working: no new content is displayed and neither restoring in-app purchases not buying the respective one via the App Store popup interface works.

Users who buy the in-app purchase have no problems at all and can restore it after uninstalling and reinstalling the app. Has anyone experienced a similar problem? Is it my fault, the plugin’s or maybe even Apples?