The '$id' and '$ref' metadata properties must be JSON strings. Current token type is 'PropertyName'

ConsoleApp.csproj

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>netcoreapp3.1</TargetFramework>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="System.Text.Json" Version="5.0.0-preview.2.20160.6" />
  </ItemGroup>

</Project>

Program.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Text;
using System.Text.Encodings.Web;
using System.Text.Json;
using System.Text.Json.Serialization;

namespace ConsoleApp30
{
    class Program
    {
        static async System.Threading.Tasks.Task Main(string[] args)
        {
            string json = @"{
                ""$id"": ""1"",
                ""$values"": [
                    {
                        ""$id"": ""2"",
                        ""location"": ""1"",
                        ""warehouses"": {
                            ""$id"": ""3"",
                            ""$values"": [
                                {
                                    ""$id"": ""4"",
                                    ""warehouse"": ""1""
                                },
                                {
                                    ""$id"": ""5"",
                                    ""warehouse"": ""2""
                                }
                            ]
                        }
                    }
                ]
            }";

            Stream stream = new MemoryStream(Encoding.UTF8.GetBytes(json));
            var opts = new JsonSerializerOptions
            {
                ReferenceHandling = ReferenceHandling.Preserve,
                PropertyNameCaseInsensitive = true,
                Encoder = JavaScriptEncoder.Default
            };

            List<Locations> locations = await JsonSerializer.DeserializeAsync<List<Locations>>(stream, opts);

            foreach(Locations location in locations)
            {
                Console.WriteLine($"Location {location.Location}");
                foreach(Warehouses warehouse in location.Warehouses)
                {
                    Console.WriteLine($"  Warehouse {warehouse.Warehouse}");
                }
            }
        }

        public class Locations
        {
            public string Location { get; set; }
            public List<Warehouses> Warehouses { get; set; }
        }

        public class Warehouses
        {
            public string Warehouse { get; set; }
        }
    }
}