GraphQL cartLinesAdd API not working

[prashants6]

When I hit this API, below is the response I get:

{

    "data": {

        "cartLinesAdd": null

    },

    "errors": [

        {

            "message": "invalid id",

            "locations": [

                {

                    "line": 3,

                    "column": 3

                }

            ],

            "path": [

                "cartLinesAdd"

            ]

        }

    ]

}

So, please check what's wrong here or which ID is invalid?