In my app (already existing for iOS), I add new game levels (in app items) every week. My question is: If my app downloads the new content from my servers, then do I really need to update my app? The docs say: "If your app update also entails an addition of or update to a purchasable item, submit your consumable, entitled, and/or subscription content prior to your update." In iOS no app update is necessary because the app can query all possible products, and only the devices of the testers and of the developer can "see" the in-app items which are under review.
You can create new IAP items in your live app and get those items tested through SDK tester in the development version of the app before submitting the new IAP items in the portal. Once the testing is done, make sure the contents associated with new items are available in your server to be fetched by the live client and then submit the new items so that once the new items are live, the live version of your app would start receiving the new items and display those in your app’s IAP catalog. This way you do not need any version update of your existing app. Thanks.
No, if you are controlling the UI of the app to show purchasable items from your app-server. You don't have to update to a new app. But make sure the IAP item is update in the developer console for your app and check if it is up and live. before the new purchasable item is shown in the app.