AK2004 - Error

IDslActor.Receive message handler delegate must not be a void async delegate. Use ReceiveAsync instead.

Cause

IDslActor.Receive accepts an Action<TMessage, IActorContext> as a delegate, any void async delegate passed as an argument will be invoked as a detached asynchronous function that can cause erroneous message processing behavior.

An example:

using Akka.Actor;
using System.Threading.Tasks;

public sealed class MyClass
{
    public MyClass(ActorSystem sys)
    {
        sys.ActorOf(act =>
        {
            act.Receive<int>(async (msg, context) =>
            {
                await Task.Yield();
                context.Sender.Tell(msg);
            });
        }, "dslActor");
    }
}

Resolution

using Akka.Actor;
using System.Threading.Tasks;

public sealed class MyClass
{
    public MyClass(ActorSystem sys)
    {
        sys.ActorOf(act =>
        {
            // Use ReceiveAsync() if you're passing an asynchronous delegate
            act.ReceiveAsync<int>(async (msg, context) =>
            {
                await Task.Yield();
                context.Sender.Tell(msg);
            });
        }, "dslActor");
    }
}