We STRONGLY RECOMMEND that you use separate IDs (in this case a separate application in the AdMob front-end) for different platforms.
You aren't getting fill on iOS because the ad unit is for a linked Android app and because your iOS package name isn't a valid iOS package (you mentioned it isn't on app store yet). Technically, a valid package might override the fact that the ad unit is for the wrong platform, and you may get fill if you just published your app. But you'll notice the following side effects if you don't create platform specific ad units:
1. Mediation won't work on iOS if you ever want to add other networks
2. No fine-grained reporting on how your iOS or Android apps are performing individually
3. Unknown behavior on setting up house ads promoting other apps. I don't think the front-end will let you associate a campaign for an iOS app download ad to an Android ad unit.
and possibly others (these were just off the top of my head).
So, please create a separate app for iOS, and a new ad unit. I'd also recommend the same for Windows.
Thanks,
Eric