Startup.cs

using LiftApi.Hubs;
using LiftApi.Models;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.HttpsPolicy;
using Microsoft.AspNetCore.SpaServices.ReactDevelopmentServer;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using System.Collections.Generic;

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

        public IConfiguration Configuration { get; }

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddSignalR();

            services.AddCors(options =>
            {
                options.AddDefaultPolicy(builder =>
                {
                    builder.WithOrigins("http://localhost:3000")
                        .AllowAnyHeader()
                        .AllowAnyMethod()
                        .AllowCredentials();
                });
            });

            services.AddControllersWithViews();
            services.AddDbContext<ApplicationDbContext>(options => options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));
            // In production, the React files will be served from this directory
            //services.AddSpaStaticFiles(configuration =>
            //{
            //    configuration.RootPath = "ClientApp/build";
            //});
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            else
            {
                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.UseSpaStaticFiles();
            app.UseCors();
            app.UseRouting();
            app.UseAuthorization();

            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllerRoute(
                    name: "default",
                    pattern: "{controller}/{action=Index}/{id?}");
                endpoints.MapHub<LiftHub>("/lifts");
            });

            //app.UseSpa(spa =>
            //{
            //    spa.Options.SourcePath = "ClientApp";

            //    if (env.IsDevelopment())
            //    {
            //        spa.UseReactDevelopmentServer(npmScript: "start");
            //    }
            //});
        }
    }
}