Go to the file page on iS.
Top right, Hover over File Details, then click on View Download History.
The page you default to is 'regular' (credit) sales, but there are also tabs for Image Subscriptions etc.
Remember, if a file sells as a sub on e.g. 1st October, it won't show up in sales, or payments, until sometime in November.
There's a script/plug-in for Chrome which some people find easier for this sort of thing, but as the APD is all over the place ATM, developers are waiting until it settles before working on updating their code.