Iran dancing couple given 10-year jail sentence

[arewethereyet]

I'm confused by the prostitution charges.  Who paid who for what?

Prostitution.
In Iranian law this is a word with a legal meaning that isn't the same than in Western countries (There are small differences between jurisdictions of the Western world).

Each jurisdictions have words to define things.
For example , in the majority of English speaking countries we use the term "First degree murder" for the act of assassination.

Assassination is a murder that was prepared before committing the act.
In most places , assassination means what said above for the legal definition of this word.

Each jurisdictions have its definition of what constitute "First degree murder" or the equivalent term.

Each jurisdictions have its legislation and regulation. What is legal in a place can be illegal in another place.
For example , gay sex between consenting adult is legal everywhere in Western world but it's illegal in many countries like Burundi , Cooks Island (Law prohibiting homosexual practice between males is de facto not enforced) , Iran etc...

That certainly clears things up.  

What does 'prostitution' mean in Iranian law?