Getting an error when connecting to SignalR

Question

I have the following code in my Blazor Server application and I am getting the following error when the SignalR service starts up
connection = new HubConnectionBuilder()
.WithUrl(nm.ToAbsoluteUri("DataHub"))
.Build();
connection.On("ReceivedSyncRecord", this.OnReceiveSync);
await InvokeAsync(StateHasChanged);

                await connection.StartAsync();

System.IO.InvalidDataException: Invalid negotiation response received. ---> System.Text.Json.JsonReaderException: '<' is an invalid start of a value. LineNumber: 2 | BytePositionInLine: 0. at System.Text.Json.ThrowHelper.ThrowJsonReaderException(Utf8JsonReader& json, ExceptionResource resource, Byte nextByte, ReadOnlySpan1 bytes) at System.Text.Json.Utf8JsonReader.ConsumeValue(Byte marker) at System.Text.Json.Utf8JsonReader.ReadFirstToken(Byte first) at System.Text.Json.Utf8JsonReader.ReadSingleSegment() at System.Text.Json.Utf8JsonReader.Read() at Microsoft.AspNetCore.Internal.SystemTextJsonExtensions.CheckRead(Utf8JsonReader& reader) at Microsoft.AspNetCore.Http.Connections.NegotiateProtocol.ParseResponse(ReadOnlySpan1 content) --- End of inner exception stack trace --- at Microsoft.AspNetCore.Http.Connections.NegotiateProtocol.ParseResponse(ReadOnlySpan`1 content) at Microsoft.AspNetCore.Http.Connections.Client.HttpConnection.NegotiateAsync(Uri url, HttpClient httpClient, ILogger logger, CancellationToken cancellationToken) at Microsoft.AspNetCore.Http.Connections.Client.HttpConnection.GetNegotiationResponseAsync(Uri uri, CancellationToken cancellationToken) at Microsoft.AspNetCore.Http.Connections.Client.HttpConnection.SelectAndStartTransport(TransferFormat transferFormat, CancellationToken cancellationToken) at Microsoft.AspNetCore.Http.Connections.Client.HttpConnection.StartAsyncCore(TransferFormat transferFormat, CancellationToken cancellationToken) at System.Threading.Tasks.ForceAsyncAwaiter.GetResult() at Microsoft.AspNetCore.Http.Connections.Client.HttpConnection.StartAsync(TransferFormat transferFormat, CancellationToken cancellationToken) at Microsoft.AspNetCore.Http.Connections.Client.HttpConnectionFactory.ConnectAsync(EndPoint endPoint, CancellationToken cancellationToken) at Microsoft.AspNetCore.Http.Connections.Client.HttpConnectionFactory.ConnectAsync(EndPoint endPoint, CancellationToken cancellationToken) at Microsoft.AspNetCore.SignalR.Client.HubConnection.StartAsyncCore(CancellationToken cancellationToken) at Microsoft.AspNetCore.SignalR.Client.HubConnection.StartAsyncInner(CancellationToken cancellationToken) at System.Threading.Tasks.ForceAsyncAwaiter.GetResult() at Microsoft.AspNetCore.SignalR.Client.HubConnection.StartAsync(CancellationToken cancellationToken) at

I used Fiddler and saw it was doing the following.

Result Protocol Host URL Body Caching Content-Type Process Comments Custom

1 502 HTTP localhost:4124 /_blazor/negotiate?negotiateVersion=1 512 no-cache, must-revalidate text/html; charset=UTF-8 chrome:18052

Do you have any Idea on how to fix this?