SharePoint: Displaying a Lookup Value in the Header on the Edit Screen

When I edit an item, I cannot see the lookup value in the header.

Here is my current JSON code:

{

"debugmode": "true",

"elmType": "div",

"attributes": {

    "class": "ms-borderColor-neutralTertiary"

},

"style": {

    "width": "99%",

    "border-top-width": "0px",

    "border-bottom-width": "1px",

    "border-left-width": "0px",

    "border-right-width": "0px",

    "border-style": "solid",

    "margin-bottom": "16px"

},

"children": [

    {

        "elmType": "div",

        "style": {

            "display": "flex",

            "box-sizing": "border-box",

            "align-items": "center"

        },

        "children": [

            {

                "elmType": "div",

                "attributes": {

                    "iconName": "DeveloperTools",

                    "class": "ms-fontSize-42 ms-fontWeight-regular  ms-fontColor-themePrimary",

                    "title": "Your icon"

                },

                "style": {

                    "flex": "none",

                    "padding": "0px",

                    "padding-left": "0px",

                    "height": "36px"

                }

            }

        ]

    },

    {

        "elmType": "div",

        "attributes": {

            "class": "ms-fontColor-neutralSecondary ms-fontWeight-bold ms-fontSize-24"

        },

        "style": {

            "box-sizing": "border-box",

            "width": "100%",

            "text-align": "left",

            "padding": "21px 12px",

            "overflow": "hidden"

        },

        "children": [

            {

                "elmType": "div",

                "txtContent": {

                    "operator": "+",

                    "operands": [

                        "Here i want see the Lookup Value:  ",

                        "([$lookupvalue])"

                    ]

                },

                "style": {

                    "height": "24px"

                }

            }

        ]

    }

]

}