Want to apply discount on header level for Order Entry in SAGE 300

Dear Expert

I am stuck in the middle of a project and it is very important project for me. Actually, we are an integration company. We are trying to create an order with header level discount from Magento 2 to SAGE 300 via REST API. 

Request Url : xxxxx-sage/.../OEOrders

Request body : 

{
  "OrderNumber""ASS1886782256009",
  "CustomerNumber""633",
  "BillToName""Customer Check",
  "BillToAddressLine1""895 Rip road",
  "BillToAddressLine2"null,
  "BillToCity""Kolkata",
  "BillToStateProvince""FL",
  "BillToZipPostalCode""56233",
  "BillToCountry""US",
  "BillToPhoneNumber""8956211222",
  
  "ShipToLocationCode""178",
  "ShipToName""JK Roy",
  "ShipToAddressLine1""561 Hi road",
  "ShipToAddressLine2"null,
  "ShipToCity""Baguiati",
  "ShipToStateProvince""FL",
  "ShipToZipPostalCode""56234",
  "ShipToCountry""US",
  "ShipToPhoneNumber""9854121212",
  "OrderTotalBeforeTax"186.2,
    "OrderInclTaxTotal"0.000,
    "OrderItemTotalAmount"186.2,
    "OrderDiscountBase"186.2,
    "OrderDiscountPercentage"0.00000,
    "OrderDiscountAmount"20,
    "OrderTotalMiscellaneousCharges"0.000,
    "OrderSubtotalAmount"166.2,
    "OrderTotalWithInvoiceDisc"166.2,
    "OrderExclTaxTotal"18.62,
    "OrderTotal"184.82,
    "OrderAmountDue"184.82,
    "OrderDiscountAmountOverride"true,
  "OrderDetails": [
    {
      "LineType""Item",
      "Item""*KL-ST1-R*",
      "QuantityOrdered"2,
      "PricingUnitPrice"93.1,
      "OrderDiscountAmount"0,
      "MiscellaneousChargesCode"null,
      "ExtendedAmount"186.2,
      "PriceOverride"true,
      "DiscountedExtendedAmount"166.2,
      "HeaderDiscount"20,
      "OrderDetailOptionalFields": [
        {
          "OptionalField""AECODRITEMID",
          "Value""190"
        }
      ]
    }
  ],
  "TaxGroup""IVAT",
  "OrderOptionalFields": [
    {
      "OptionalField""AECORDID",
      "Value""156"
    },
    {
      "OptionalField""AECORDPMMTHD",
      "Value""checkmo"
    }
  ]
}
I have provided the discount amount to "OrderDiscountAmount" on header level,  "DiscountedExtendedAmount" and "HeaderDiscount" on line level. 
But, the applied discount is not reflecting to SAGE order on header level. 
Please help on urgent basis.
Thanks
Avijit