There's a case of sending funds to a custom payee (e.g. not receiving them, but rather proxying the payment to another payee), described as an API example here. I'm curious, who is liable for such a transaction (e.g. who's being help responsible for a possible refund) - the proxy or the payee? What would be the procedure in case of a fraudulent payee/payees? Is the proxy responsible for mediating a transaction, or the whole responsibility is being held by the payee?