Cors issue with .NET Core, Angular, Signalr, and AWS

I am using Angular 8 client to connect to an AWS beanstalk hosted .NET Core API that runs Signalr.

This code was all running perfectly fine while I was running my Angular app locally. But as soon as I pushed it up to be hosted, I started getting errors.

I am getting this error

My .NET Core connection looks like this

// Startup.cs

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using SignalRHub;

namespace SignalR_Hub
{
    public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        public IConfiguration Configuration { get; }

        public void ConfigureServices(IServiceCollection services)
        {
            services.AddCors(o => o.AddPolicy("CorsPolicy", builder =>
            {
                builder
                .AllowAnyMethod()
                .AllowAnyHeader()
                .AllowCredentials()
                .WithOrigins("http://<my-site>.com/"); //<my-site> is replaced with the correct domain.
            }));

            services.AddSignalR();

            services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_2);
        }

        public void Configure(IApplicationBuilder app, IHostingEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }

            app.UseCors("CorsPolicy");
            app.UseSignalR(routes =>
            {
                routes.MapHub<NotifyHub>("/notify");
            });

            app.UseMvc();
        }
    }
}

using Microsoft.AspNetCore.Cors;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.SignalR;
using SignalRHub;
using System;

namespace SignalR_Hub.Controllers
{
    [Route("api/[controller]")]
    [ApiController]
    [EnableCors("MyPolicy")]
    public class MessageController : ControllerBase
    {
        private IHubContext<NotifyHub, ITypedHubClient> _hubContext;

        public MessageController(IHubContext<NotifyHub, ITypedHubClient> hubContext)
        {
            _hubContext = hubContext;
        }

        [HttpPost]
        public string Post([FromBody]Message msg)
        {
            string retMessage;

            try
            {
                _hubContext.Clients.All.BroadcastMessage(msg.Type, msg.Payload);
                retMessage = "Success";
            }
            catch (Exception e)
            {
                retMessage = e.ToString();
            }

            return retMessage;
        }
    }
}

My Angular setup looks like this:

import { Component, OnInit } from '@angular/core';
import { MessageService } from 'primeng/api';

import * as signalR from '@aspnet/signalr';

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css'],
  providers: [MessageService]
})
export class AppComponent implements OnInit {

  constructor(private messageService: MessageService) { }

  ngOnInit(): void {
    const connection = new signalR.HubConnectionBuilder()
      .configureLogging(signalR.LogLevel.Information)
      .withUrl('http://<my-aws-setup>.elasticbeanstalk.com/notify')
      .build();

    connection.start().then(function () {
      console.log('Connected!');
    }).catch(function (err) {
      return console.error(err.toString());
    });

    connection.on('BroadcastMessage', (type: string, payload: string) => {
      this.messageService.add({ severity: type, summary: payload, detail: 'Via SignalR' });
    });
  }
}

I made sure that there is nothing in my AWS s3 setup for Cors.

Some things I have tried:

• Removed Cors from API code, added Cors policy into AWS s3.
• In the Startup.cs I had .AllowAnyOrigins().
• I tried specifying that header, that didnt seem to do anything.

I pushed all my latest code to github here: Client API