Cómo implementar Relay en Unity para jugar multijugador por internet

using System.Linq;
using System.Threading.Tasks;
using Unity.Netcode;
using Unity.Netcode.Transports.UTP;
using Unity.Networking.Transport.Relay;
using Unity.Services.Authentication;
using Unity.Services.Core;
using Unity.Services.Relay;
using UnityEngine;

public class RelayManager : MonoBehaviour
{
    public static RelayManager Instance { get; private set; }
    public string JoinCode { get; private set; }

    void Awake()
    {
        if (Instance != null) { Destroy(gameObject); return; }
        Instance = this;
    }

    public async Task InitializeAsync()
    {
        await UnityServices.InitializeAsync();
        if (!AuthenticationService.Instance.IsSignedIn)
            await AuthenticationService.Instance.SignInAnonymouslyAsync();
    }

    public async Task<string> StartHostWithRelay(int maxPlayers = 4)
    {
        // Reservar espacio en Relay (maxPlayers - 1 porque el Host ocupa un slot)
        var allocation = await RelayService.Instance.CreateAllocationAsync(maxPlayers - 1);
        JoinCode = await RelayService.Instance.GetJoinCodeAsync(allocation.AllocationId);

        // Configurar transporte
        var endpoint = allocation.ServerEndpoints.First(e => e.ConnectionType == "dtls");
        var serverData = new RelayServerData(
            endpoint.Host, (ushort)endpoint.Port,
            allocation.AllocationIdBytes, allocation.ConnectionData,
            allocation.ConnectionData, allocation.Key, true);

        NetworkManager.Singleton.GetComponent<UnityTransport>().SetRelayServerData(serverData);
        NetworkManager.Singleton.StartHost();
        return JoinCode;
    }

    public async Task StartClientWithRelay(string joinCode)
    {
        var joinAllocation = await RelayService.Instance.JoinAllocationAsync(joinCode);

        // IMPORTANTE: el 5to parametro es HostConnectionData, no ConnectionData
        var endpoint = joinAllocation.ServerEndpoints.First(e => e.ConnectionType == "dtls");
        var serverData = new RelayServerData(
            endpoint.Host, (ushort)endpoint.Port,
            joinAllocation.AllocationIdBytes, joinAllocation.ConnectionData,
            joinAllocation.HostConnectionData, joinAllocation.Key, true);

        NetworkManager.Singleton.GetComponent<UnityTransport>().SetRelayServerData(serverData);
        NetworkManager.Singleton.StartClient();
    }
}

async void Start()
{
    await RelayManager.Instance.InitializeAsync();
}

// Boton crear partida
async void OnHost()
{
    var code = await RelayManager.Instance.StartHostWithRelay();
    // Mostrar 'code' en pantalla para que lo comparta
}

// Boton unirse
async void OnJoin()
{
    var code = codeInput.text.Trim().ToUpper();
    await RelayManager.Instance.StartClientWithRelay(code);
}