Insert a new dynamic record in JSON under array field

As I said in my previous reply, enable Pass through in the Mapper. You’ll get the following result:

  {
    "entity": {
      "attributes": {
        "type": "CustomField",
        "url": "A"
      },
      "Metadata": {
        "valueSet": {
          "value": [
            {
              "color": null,
              "default": false,
              "description": null,
              "isActive": null,
              "label": "None",
              "urls": null,
              "valueName": "None"
            },
            {
              "color": null,
              "default": false,
              "description": null,
              "isActive": null,
              "label": "Country",
              "urls": null,
              "valueName": "Country"
            },
            {
              "color": null,
              "default": false,
              "description": null,
              "isActive": null,
              "label": "Employee",
              "urls": null,
              "valueName": "Employee"
            },
            {
              "color": null,
              "default": false,
              "description": null,
              "isActive": null,
              "label": "Both",
              "urls": null,
              "valueName": "Both"
            },
            {
              "color": null,
              "default": false,
              "description": null,
              "isActive": null,
              "label": "Active",
              "urls": null,
              "valueName": "Active"
            }
          ]
        }
      }
    }
  }
]