I'm doing a REST API call to get the global value set and trying to deserialize the JSON result to get the picklist values in a List<String>.

Here is the JSON:

{
  "size": 1,
  "totalSize": 1,
  "done": true,
  "queryLocator": null,
  "entityTypeName": "GlobalValueSet",
  "records": [
    {
      "attributes": {
        "type": "GlobalValueSet",
        "url": "/services/data/v53.0/tooling/sobjects/GlobalValueSet/0Nt59000000AAAAAAA"
      },
      "Metadata": {
        "customValue": [
          {
            "color": null,
            "default": false,
            "description": null,
            "isActive": null,
            "label": "USA",
            "urls": null,
            "valueName": "USA"
          },
          {
            "color": null,
            "default": false,
            "description": null,
            "isActive": null,
            "label": "Canada",
            "urls": null,
            "valueName": "Canada"
          }
        ],
        "description": null,
        "masterLabel": "US States & Territories",
        "sorted": false,
        "urls": null
      },
      "Id": "0Nt59000000AAAAAAA"
    }
  ]
}

Error: System.JSONException: Malformed JSON: Expected '{' at the beginning of an object.

Here is what I have tried so far:

Wrapper:
    public class GlobalValueSetWrapper{
        Metadata metadata;

    public class Metadata {
        public List<CustomValue> customValue;
    }
    
    public class CustomValue {
        public String label;  
        public String valueName;
    }
    }


Class:
//calling API to get the JSON result
HttpResponse res = GlobalValueSetAPIHandler.getResponse('Countries');
GlobalValueSetWrapper wrapper = (GlobalValueSetWrapper) JSON.deserialize(res.getBody(), GlobalValueSetWrapper.class);