transferring apps from iphone to ipad

The terms for the app store include that content may be withdrawn or simply no longer available. There is nothing you can do; you cannot transfer it. There could be several reasons for it no longer being available; the best you can do is to contact the developer and ask them about it.

If the app is compatible with both, you can download it on the other device. You cannot "transfer" it.

App has been removed from the app store, but exists on iPad and in library. Can no longer find apps from iTunes.