Getting User Not Found when reading conversations

I am getting user not found while trying to get all conversations.

Trying to execute it through Postman and passing authorization bearer as well.

URL - https://api.intercom.io/conversations

'Authorization': 'Bearer <ACCESS_TOKEN>

'Content-Type': 'application/json',

Postman response -

{
    "type": "error.list",
    "request_id": "003rmrddranpjr8ds4lg",
    "errors": [
        {
            "code": "not_found",
            "message": "User Not Found"
        }
    ]
}