I'm currently in the process of submitting a new app with a single non-consumable In-App Purchase.
After creating the IAP in AppStore Connect, I created a synced StoreKit config in Xcode which correctly loaded the purchase.
After making sure that the transaction works as expected within the app, I submitted the app in AppStore connect, including the In-App Purchase.
Since then, the In-App Purchase can not be found in the StoreKit configuration and isn't displayed in the app, which lead to the submission being rejected.
As requested by the review team, I have resubmitted the In-App Purchase, so it's currently "Waiting for Review" but still not showing up in the StoreKit configuration in Xcode.
I'm not quite sure what I'm doing wrong here. I have other apps live in the AppStore with IAPs and no outstanding agreements to sign.