Impossible to restore your purchase

Its a good but expensive app. I bought this app on my iPad and would expect to be able to restore the app on my iPhone. But it doesnt allow me. I also read that other users cant restore the app on the same devise they bought it. For the price of the app I would expect a better service. It seems that once they got your money, they dont want to help you anymore!

Myukis@n about Go Talk - Learn languages, v2.3.0