REST API: how do I attach a payment to an order and return the unpaid balance?

Currently, I doing this PUT method but it doesn’t do anything but return the sales order object:

https://sandbox.com/AcumaticaERP/entity/Default/22.200.001/SalesOrder?$expand=Payments&$select=Payments/AppliedToOrder:

{

    "OrderType": {"value": "WB"},

    "OrderNbr": {"value": "WB00159383"},

    "Payments": [

        {

            "ReferenceNbr": {

                "value": "598095"

            }

        }

    ]        

}

I’m expecting it to return the unpaid balance on the order so I can use this amount to call the same method with the following body:

{

    "OrderType": {"value": "WB"},

    "OrderNbr": {"value": "WB00159383"},

    "Payments": [

        {

            "ReferenceNbr": {

                "value": "787266"

            },

            "AppliedToOrder": {

                "value": 55.5900

            }

        }

    ]        

}