ASP.NET Core 6 how can I Use a .pem-chain file or .pem file to set up https

Question

I have an app I have written in asp.net core 6, and I think I have what I need to get https set up. I have a .pem-chain file and a .pem file I can use and I also have a .key file that was created when I generated a .csr file.

I looked through all the Documentation I could find regarding this.

This is the one that seemed the most relevant but there is no mention of any of those file types exactly, it mentions using .UseHttps(<pem filename>,<key filename>) but that throws

Unhandled exception. System.NotSupportedException: The server mode SSL must use a certificate with the associated private key.
   at System.Net.Security.SslStreamCertificateContext.Create(X509Certificate2 target, X509Certificate2Collection additionalCertificates, Boolean offline, SslCertificateTrust trust)
   at Microsoft.AspNetCore.Server.Kestrel.Https.Internal.HttpsConnectionMiddleware..ctor(ConnectionDelegate next, HttpsConnectionAdapterOptions options, ILoggerFactory loggerFactory)
   at Microsoft.AspNetCore.Hosting.ListenOptionsHttpsExtensions.<>c__DisplayClass12_0.<UseHttps>b__0(ConnectionDelegate next)
   at Microsoft.AspNetCore.Server.Kestrel.Core.ListenOptions.Build()
   at Microsoft.AspNetCore.Server.Kestrel.Core.KestrelServerImpl.<>c__DisplayClass30_0`1.<<StartAsync>g__OnBind|0>d.MoveNext()
--- End of stack trace from previous location ---
   at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.AddressBinder.BindEndpointAsync(ListenOptions endpoint, AddressBindContext context, CancellationToken cancellationToken)
   at Microsoft.AspNetCore.Server.Kestrel.Core.ListenOptions.BindAsync(AddressBindContext context, CancellationToken cancellationToken)
   at Microsoft.AspNetCore.Server.Kestrel.Core.AnyIPListenOptions.BindAsync(AddressBindContext context, CancellationToken cancellationToken)
   at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.AddressBinder.AddressesStrategy.BindAsync(AddressBindContext context, CancellationToken cancellationToken)
   at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.AddressBinder.BindAsync(IEnumerable`1 listenOptions, AddressBindContext context, CancellationToken cancellationToken)
   at Microsoft.AspNetCore.Server.Kestrel.Core.KestrelServerImpl.BindAsync(CancellationToken cancellationToken)
   at Microsoft.AspNetCore.Server.Kestrel.Core.KestrelServerImpl.StartAsync[TContext](IHttpApplication`1 application, CancellationToken cancellationToken)
   at Microsoft.AspNetCore.Hosting.GenericWebHostService.StartAsync(CancellationToken cancellationToken)
   at Microsoft.Extensions.Hosting.Internal.Host.StartAsync(CancellationToken cancellationToken)
   at Microsoft.Extensions.Hosting.HostingAbstractionsHostExtensions.RunAsync(IHost host, CancellationToken token)
   at Microsoft.Extensions.Hosting.HostingAbstractionsHostExtensions.RunAsync(IHost host, CancellationToken token)
   at Microsoft.Extensions.Hosting.HostingAbstractionsHostExtensions.Run(IHost host)
   at Microsoft.AspNetCore.Builder.WebApplication.Run(String url)
   at Program.<Main>$(String[] args) in C:\Users\Nicole\source\repos\TestWebAppRazor\TestWebAppRazor\Program.cs:line 43

Here is my Program.cs

using Microsoft.AspNetCore.Authentication.Certificate;
using Microsoft.AspNetCore.Server.Kestrel.Https;
using Microsoft.AspNetCore.Server.Kestrel.Core;
using Microsoft.AspNetCore.Hosting;

var builder = WebApplication.CreateBuilder(args);
// Add services to the container.
builder.Services.AddRazorPages();
builder.WebHost.ConfigureKestrel(serverOptions =>
{
    serverOptions.ConfigureEndpointDefaults(listenOptions =>
    {
        listenOptions.UseHttps("mywebsite_com.pem", "mywebsite.com.key");
    });
});
builder.Services.Configure<KestrelServerOptions>(options =>
{
    options.ConfigureHttpsDefaults(options =>
        options.ClientCertificateMode = ClientCertificateMode.RequireCertificate);
});
builder.Services.AddAuthentication(CertificateAuthenticationDefaults.AuthenticationScheme).AddCertificate();
builder.Host.UseSystemd();
var app = builder.Build();

// Configure the HTTP request pipeline.
if (!app.Environment.IsDevelopment())
{
    app.UseExceptionHandler("/Error");
    // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
    app.UseHsts();
}

app.UseHttpsRedirection();
app.UseStaticFiles();

app.UseRouting();

app.UseAuthorization();
app.UseAuthentication();

app.MapRazorPages();

app.Run();

I know I am doing things wrong but I am having a difficult time deciphering the documentation.

Any guidance or direction of where to look for documentation to work with what I have would be greatly appreciated.