Purchase Order update quantity Rest url do not show approval action on UI

Hi,

I have a requirement to update quantity on the purchase order.

We are using below Rest URL for the same .

/fscmRestApi/resources/latest/draftPurchaseOrders/POHEADERID 

Payload:

{

    "ChangeOrderDescription": "change order",

    "ChangeOrderInitiatingParty": "BUYER",

    "lines": [

    {

        "POLineId": 12005,

        "Quantity": 5

    }

    ]

}

Above Rest is able to update quantity but it do not show approval action/next action on page ones quantity gets updated with change order .