Hi @DharmandarKumar ,

Please follow the below steps to add the approve and Reject action on the endpoint. By default, We don't have the action for the purchase order entity.

• Open the Webservice endpoint screen
• Select the Endpoint and select the Entity “Purchase Order”
• Expand the entity and select Actions and click on the Insert button on the top on top.
• A popup will open. Select the action “Approve” from the selector
• And click on OK. If the name already exists, rename the action name.
• Do the same for Reject action.

Now you can try from the postman. You can able to approve /reject the PO Order.
 

Please try like below on the postman.

Url - Instanceurl/entity/TEST/20.200.001/PurchaseOrder/POApprove
Method  - Post

Request

{

    "entity": {

        "Type": {

            "value": "Normal"

        },

        "OrderNbr": {

            "value": "PO001587"

        }

    },

    "parameters": {}

}