RuntimeBinderException: Convert type System.Threading.Tasks.Task<object> to string - type-conversion

Question

I do an example with signalR. But it doesn't function because of one mistake.
The one mistake (can not convert type system.threading.tasks.task< object> to string) is in this line:
return context.Clients.All.RecieveNotification(simple);
It is at the bottom of the code you can see below.
Below you see the method I wrote. There I do a connection with the database and get the content with a command/query.
Then a few checks and also SqlDependency.
public string SendNotifications()
{
using (var connection = new SqlConnection(ConfigurationManager.ConnectionStrings["DefaultConnection"].ConnectionString))
{
string query = "SELECT eintrag FROM [dbo].[simple_column]";
connection.Open();
using (SqlCommand command = new SqlCommand(query, connection))
{
command.Notification = null;
DataTable dt = new DataTable();
SqlDependency dependency = new SqlDependency(command);
dependency.OnChange += new OnChangeEventHandler(dependency_OnChange);
if (connection.State == ConnectionState.Closed)
connection.Open();
var reader = command.ExecuteReader();
dt.Load(reader);
if (dt.Rows.Count > 0)
{
simple = dt.Rows[0]["eintrag"].ToString();
}
}
}
IHubContext context = GlobalHost.ConnectionManager.GetHubContext<NotificationHub>();
return context.Clients.All.RecieveNotification(simple);
}
And here I use the function:
var notifications = $.connection.notificationHub;
notifications.client.recieveNotification = function (simple) {
// Add the message to the page.
$('#dbMessage').text(simple);
};
I hope you can help me.
Thanks.