The app works fine on an iPad, but to find it in the App Store on an iPad you have to:
1) Search for you app using you app name like you would normally — the search will fail, but the Filters option will appear to the left of the search box
2) Click Filters, select Supports and select iPhone only
3) Your app will now appear and can be downloaded and run on the iPad.
To avoid all this, you can go to the Promote App section of the cockpit, get the intelligent download link and just email users this link for example
and if they click it on their email on the iPad, it will take them straight to the app in the App Store and they can download it…