var groupProvider = new RemoteGroupProvider(
    DynamicInMemoryProxyFactory.Instance,
    DynamicRemoteProxyFactory.Instance,
    new TestJsonRemoteSerializer(),
    new RemoteClientResultPendingTaskRegistry());

using var group = groupProvider.GetOrAddGroup<int, IReceiver>("name");
await group.AddAsync(0, new Receiver(100));

var receiver = group.Single(0);

// Throws System.NotSupportedException: 'In-memory proxy does not support to invoke multiple receivers.'
var x = await receiver.NotifyAsync().ConfigureAwait(false);

Console.WriteLine($"Received: {x}");

public interface IReceiver
{
    Task<int> NotifyAsync();
}

class Receiver(int value) : IReceiver
{
    public Task<int> NotifyAsync()
    {
        Console.WriteLine("Notify");
        return Task.FromResult(value);
    }
}