Okta aspnet mvc example bug

Downloaded the aspnet mvc example from here: https://github.com/oktadeveloper/okta-aspnet-mvc-example
Modified the settings in web.config to:

<add key="okta:ClientId" value="myclientid" />
<add key="okta:ClientSecret" value="MyKey />
<add key="okta:OrgUri" value="https://my.oktapreview.com" />

<!-- 2. Update the Okta application with these values -->
<add key="okta:RedirectUri" value="http://localhost:64389/authorization-code/callback" />
<add key="okta:PostLogoutRedirectUri" value="http://localhost:64389/Account/PostLogout" />

When I run an exception is thrown in the startup.cs file. Specifically, the call to:

tokenClient.RequestAuthorizationCodeAsync(n.Code, redirectUri);

throws an exception. “Not Found”

The stack trace follows:

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.Exception: Not Found

Source Error:

Line 60: if (tokenResponse.IsError)
Line 61: {
Line 62: throw new Exception(tokenResponse.Error);
Line 63: }
Line 64:

Source File: C:\Dev\Research\Okta\Okta Sample Thiers\OktaAspNetExample\Startup.cs Line: 62

Stack Trace:

[Exception: Not Found]
OktaAspNetExample.<b__5_0>d.MoveNext() in C:\Dev\Research\Okta\Okta Sample Thiers\OktaAspNetExample\Startup.cs:62
System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) +99
System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) +61
System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd(Task task) +25
Microsoft.Owin.Security.OpenIdConnect.d__1a.MoveNext() +5109
System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() +26
Microsoft.Owin.Security.OpenIdConnect.d__1a.MoveNext() +6433
System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) +99
System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) +61
Microsoft.Owin.Security.Infrastructure.d__0.MoveNext() +571
System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) +99
System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) +61
Microsoft.Owin.Security.Infrastructure.d__0.MoveNext() +255
System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) +99
System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) +61
Microsoft.Owin.Host.SystemWeb.IntegratedPipeline.d__5.MoveNext() +182
System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) +99
System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) +61
Microsoft.Owin.Security.Infrastructure.d__0.MoveNext() +638
System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) +99
System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) +61
Microsoft.Owin.Host.SystemWeb.IntegratedPipeline.d__5.MoveNext() +182
System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) +99
System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) +61
Microsoft.Owin.Host.SystemWeb.IntegratedPipeline.d__2.MoveNext() +180
Microsoft.Owin.Host.SystemWeb.IntegratedPipeline.StageAsyncResult.End(IAsyncResult ar) +69
Microsoft.Owin.Host.SystemWeb.IntegratedPipeline.IntegratedPipelineContext.EndFinalWork(IAsyncResult ar) +64
System.Web.AsyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +483
System.Web.HttpApplication.ExecuteStepImpl(IExecutionStep step) +132
System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +163