Best app develop software for audio downloads (as in-app purchases)?

Hello,

I just checked the latest reviews on some app develop software like Como, Biznessapps, Shoutem,... but hard to find this feature:

I would like to have extremely simple one-click in-app purchases. Same way like Amazon Kindle uses to sell more books on their readers: You can see the picture and description of a book, one click, and it's paid and already starts to download. With another click you can start to read your new purchase. Instead of a reader app it would be an audio player.

All what I have found so far are cart-based systems. Much too complicated for the user, they will need many clicks to download a single file.

Who knows which software makes this possible?

Thanks a lot for every hint!
Nils