You can test locally with a StoreKit configuration file without submitting to the App Store. I haven't used Sandbox so can't comment on that. You either need to sync the configuration file with appstoreconnect or add them locally to an unsynced config file. The products won't sync unless they are all ready to submit themselves. I found that to get them to this status you had to add a screenshot (any screenshot) and some review notes for each product. Once I did that they changed to a ready to submit status.