It's a private API at the moment and I don't know what our plan is on exposing that information.
You can get access to it if you use cookie-based authentication, and can reverse engineer the API. Keep in mind, we don't promise to keep the payments API stable and might break things on you, so use the API at your own risk.
Oooh, nice. I think that could work for me. I just need machine-readable versions of the Payouts data so I can reconcile cash receipts against our bookkeeping system. This is an in-house app for one company where I work full-time, so I'm not too worried about the data format changing. Will need to play around with that idea, thanks for the suggestion!