SignalR HubConnection.On<>() ambiguous error

Question

CS0121: The call is ambiguous between the following methods or properties: 'HubConnectionExtensions.On( HubConnection, string, Action)' and 'HubConnectionExtensions.On(HubConnection, string, Func<T1, Task>)'

  Connection.On<ViewAcknowledgementRequestSpecifier>("ReceiveAcknowledgementRequest", ReceiveAcknowledgementRequest);
            Connection.On<ViewDelayRequestSpecifier>("ReceiveDelayRequest", ReceiveDelayRequest);
            Connection.On<InfoRequestSpecifier>("ReceiveInfoRequest", ReceiveInfoRequest);