How to enable cors in ASP.NET core 3.0

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ASP.NET-Core

Hi,
I trying enable cors in asp.net core 3.0
I added following code to ConfigureServices in Startup.cs

services.AddCors(options =>
{
 options.AddDefaultPolicy(
 builder =>
  {
 builder.WithOrigins("https://ogrencievi.net")
.AllowAnyOrigin()
.AllowAnyHeader()
.AllowAnyMethod();
 });
});

and Configure;

app.UseCors();

Startup.cs;

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.AddCors(options =>
            {
                options.AddDefaultPolicy(
                    builder =>
                    {
                        builder.WithOrigins("https://ogrencievi.net").AllowAnyOrigin().AllowAnyHeader().AllowAnyMethod();
                    });
            });
            services.AddDbContext<OEDBContext>(_ => _.UseSqlServer("Data Source=.... Initial Database=ogrencievidb.mdf;Integrated Security=false; User ID=..;Password=...; MultipleActiveResultSets=True;"));

            services.Configure<AuthOptions>(Configuration.GetSection("AuthOptions"));

            var authOptions = Configuration.GetSection("AuthOptions").Get<AuthOptions>();


            services.AddAuthentication(options =>
            {
                options.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme;
                options.DefaultChallengeScheme = JwtBearerDefaults.AuthenticationScheme;
            }).AddJwtBearer(options =>
            {
                options.TokenValidationParameters = new TokenValidationParameters
                {
                    ValidateIssuer = true,
                    ValidateAudience = true,
                    ValidateLifetime = true,
                    RequireExpirationTime = true,
                    ValidIssuer = authOptions.Issuer,
                    ValidAudience = authOptions.Audience,
                    IssuerSigningKey = new SymmetricSecurityKey(Encoding.UTF8.GetBytes(authOptions.SecureKey)),
                    ClockSkew = TimeSpan.Zero,
                };
            });

            services.AddControllers();
        }

        // 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();
            }

            app.UseRouting();
            app.UseCors();
            app.UseAuthentication();
            app.UseAuthorization();
            app.UseHttpsRedirection();

            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllers();
            });
        }
    }

The project working on api.ogrencievi.net and this code should add the Access-Control-Allow-Origin feature to HEADERS section but it doesn't work.
How can I fix it ?

What I have tried:

I did this by looking at this link.
https://docs.microsoft.com/tr-tr/aspnet/core/security/cors?view=aspnetcore-3.0 | Microsoft Docs[^]>

I also examined this page and tried to implement it;
c# - How to enable CORS in ASP.net Core WebAPI - Stack Overflow[^]