SignalR hubConnectionBuilder issue

I'm new to Signalr. I am in my blazor client project and have made a package reference to:

Microsoft.AspNetCore.SignalR.Client.Core(8.0.4)

in my code behind file I have declared:

private HubConnection? hubConnection;

and then in my OnInitializedAsync event I have:

 hubConnection = new HubConnectionBuilder().WithUrl(Navigation.ToAbsoluteUri("/notificationhub")).Build();

VS redlines the WithUrl stating that HubConnectionBuilder does not contain a defenition for WithUrl and no accessible extension method.....

All examples that I've found including the Microsoft documentation shows this call built as above. What am I missing?