Downloaded an iPhone app on my iPad, now it's telling me I have to pay again on the iPhone

I just downloaded a 69p app on my iPad, bearing in mind it's listed as an iPhone app.

When I go onto my iPhone, there is no option to simply 'install' on there, and wants me to pay the 69p once again.

I have the new iTunes and figured I may be able to transfer purchased items on the iPad to the computer but I haven't figured out how to do it yet on the new interface.

Many thanks if someone can help

Laura