active-directory-b2c-dotnetcore-webapp | NET Core web application that can sign in a user | Azure library

Could anyone provide some insight or new links on using Azure B2C with MVC, .NET Core 3.1. Most examples are based on Core 2.2

https://docs.microsoft.com/en-us/samples/azure-samples/active-directory-b2c-dotnetcore-webapp/an-aspnet-core-web-app-with-azure-ad-b2c/

However, it seems more than a few things are done differently with 3.1.

The error I encounter in 2.2 is:

System.ArgumentNullException: Value cannot be null. (Parameter 'uriString') at System.Uri..ctor(String uriString) at Microsoft.AspNetCore.Authentication.AzureADB2C.UI.AzureADB2COpenIdConnectOptionsConfiguration.BuildAuthority(AzureADB2COptions AzureADB2COptions) at Microsoft.AspNetCore.Authentication.AzureADB2C.UI.AzureADB2COpenIdConnectOptionsConfiguration.Configure(String name, OpenIdConnectOptions options) at Microsoft.Extensions.Options.OptionsFactory1.Create(String name) at Microsoft.Extensions.Options.OptionsMonitor1.<>c__DisplayClass11_0.b__0() at System.Lazy1.ViaFactory(LazyThreadSafetyMode mode) at System.Lazy1.ExecutionAndPublication(LazyHelper executionAndPublication, Boolean useDefaultConstructor) at System.Lazy1.CreateValue() at System.Lazy1.get_Value() at Microsoft.Extensions.Options.OptionsCache1.GetOrAdd(String name, Func1 createOptions) at Microsoft.Extensions.Options.OptionsMonitor1.Get(String name) at Microsoft.AspNetCore.Authentication.AuthenticationHandler1.InitializeAsync(AuthenticationScheme scheme, HttpContext context) at Microsoft.AspNetCore.Authentication.AuthenticationHandlerProvider.GetHandlerAsync(HttpContext context, String authenticationScheme) at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.Invoke(HttpContext context) at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext context)