Update task assignee using BPM Rest API

Summary:

I want to update task assignee using this REST Endpoint "https://xxxxxxxxx.oraclecloud.com/bpm/api/4.0/tasks/{id}".

Content (please ensure you mask any confidential information):

I am getting this error.

Version (include the version you are using, if applicable):

Code Snippet (add any code snippets that support your topic, if applicable):

Request Payload:

{

    "action": {

        "id": "REASSIGN"

    },

    "assignees":[

        {

            "id":"Dummy User",

            "type":"user"

        }

    ]

}