POST https://api.sandbox.ebay.com/post-order/v2/return/5********4/mark_refund_sent
{ 
  "refundDetail":
  { 
    "itemizedRefundDetail": [
      {
        "refundAmount":
        { 
          "currency": "AUD",
          "value": "40.0"
        },
        "refundFeeType": "PURCHASE_PRICE",
        "restockingFeePercentage": "0"
      },
      { 
        "refundAmount":
        { 
          "currency": "AUD",
          "value": "3.1"
        },
        "refundFeeType": "ORIGINAL_SHIPPING",
        "restockingFeePercentage": "0"
      }
    ],
    "totalAmount":
    { 
        "currency": "AUD",
        "value": "43.1"
    }
  }
}