No overload for method 'Subscribe' takes 3 arguments

[chopin1998]

    {
    IObservable<Item> observable = minio.ListObjectsAsync(listArgs);
    IDisposable subscription = observable.Subscribe(
            item => bucketList.Add(item.Key),
            ex => Debug.LogError(ex),
            () => Debug.Log("Listed all objects in bucket " + BucketNAME + "\n"));
    }

my code like this, compiler said:

IDisposable IObservable.Subscribe(IObserver observer) No overload for method 'Subscribe' takes 3 arguments [Assembly-CSharp]

[chopin1998]

it seems that i have to define a class IObserver, then new a object as paramets to (observable.Subscribe)