Testing with testflight the IAP work with sandbox. But Apple Review was rejected. It was explained that the IAP could not be found. I cancelled the review, added the IAP to all countries again. The IAPs are in status waiting for review. Now when preparing the version, I cannot choose anymore the IAP. I don't find the option anymore to add the IAP products on the version page. Contracts are all active and in the app for me and others it is working.