Walmart Shipment API give internal server error

Question

I am implementing Walmart Shipment API as below and getting Walmart system internal error. I have check all headers are correct as i am able to generate token which is working in getOrders API but in shipment API it is not working.

API URL : https://sandbox.walmartapis.com/v3/orders/{PurchaseOrderId}/ship

Headers

Authorization : Basic Base64_Encode(clientId:clientSecret)

WM_SEC.ACCESS_TOKEN: <walmart_access_token>

WM_QOS.CORRELATION_ID : Unique Id

WM_SVC.NAME: Walmart Marketplace

WM_MARKET: mx

WM_CONSUMER.CHANNEL.TYPE: Walmart

grant_type: test

{
  "shipments": [
    {
      "shipmentLines": [
        {
          "primeLineNo": "2",
          "shipmentLineNo": "2",
          "quantity": {
            "unitOfMeasurement": "EACH",
            "amount": "2"
          }
        }
      ],
      "trackingNumber": "1234556",
      "trackingURL": "http://www.otherCarrier.com",
      "carrier": "Other"
    }
  ]
}

==============Response===============

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<ns2:errors xmlns:ns2="http://walmart.com/">
    <ns2:error>
        <ns2:code>SYSTEM_ERROR.GMP_GATEWAY_API</ns2:code>
        <ns2:field>InternalServerError</ns2:field>
        <ns2:description>Internal Server Error</ns2:description>
        <ns2:info>System encountered some internal error.</ns2:info>
        <ns2:severity>ERROR</ns2:severity>
        <ns2:category>SYSTEM</ns2:category>
        <ns2:causes/>
        <ns2:errorIdentifiers/>
    </ns2:error>
</ns2:errors>