Sample response

APIService.java

@GET("/v1/categories")
void getMessages(Callback<BaseResponse<CategoriesResponse>> callback);

CategoriesResponse.java

public class CategoriesResponse extends BaseResponse<List<Message>> {
     @SerializedName("categories") List<Category> categories;
}

Category.java

public class Category {
  private String id;
  private String name;
  private String color;
  private String icon;
  
}

Response.java

public class BaseResponse<T> {
     @SerializedName("data") public T data;
}

response.json

{
    "data": [
        {
            "object": "Category",
            "id": "zekYVdBgoA",
            "name": "Spaghetti",
            "color": "#00ff0c",
            "icon": "http://192.168.1.127:8000/storage/icons/5aa787271dd44.png",
            "created_at": {
                "date": "2018-03-13 08:09:11.000000",
                "timezone_type": 3,
                "timezone": "UTC"
            },
            "updated_at": {
                "date": "2018-03-13 08:09:11.000000",
                "timezone_type": 3,
                "timezone": "UTC"
            },
            "readable_created_at": "2 weeks ago",
            "readable_updated_at": "2 weeks ago"
        }
  ]
}