The side paying reparations is the side that lost the war.
That's usually true. And yet... after WWII, the US paid a lot of money to rebuild Germany and Japan. Do I think that's what's going on here? No, I don't. Nor do I think that the money is real. (If it is, it sounds like it's coming from the Gulf states - essentially "please stop blowing us up" money.)
But here, Iran's government has not been overthrown nor their nation occupied.