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3天前关闭。
我正在做一个使用React前端和ASP.NET后端的全栈项目（使用Visual Studio社区IDE）。我得到了CORS错误，我不知道如何修复。
我在React中调用了以下API：

const sendEmail = async(event) => {
        event.preventDefault();
        let baseUrl = '...some base url';
        let emailAddress = email.email_address;
        let emailMessage = emailText.message;
        let emailData = {
            "Id": "demo",
            "Amount": 37200,
            "Sig": "YTdjfyDBFNAKdufyBAiPPeefKLdjnf",
            "emailAddress": emailAddress,
            "notes": emailMessage
        };
        await fetch(`${baseUrl}/api/Email/Send`,{
            method: 'POST',
            headers: {
                'Content-Type': 'application/json'
            },
            body: JSON.stringify(emailData)
        })
        .then((res)=> res.json())
        .then((data) => console.log(data))
        .catch((err) => console.log(err));
    };

并且我从ASP.NET后端收到以下错误：
CORS策略已阻止从源"https：//localhost：44493"在... "/api/Email/Send "中提取的访问权限：对印前检查请求的响应未通过访问控制检查：请求的资源上不存在"Access-Control-Allow-Origin"标头。如果不透明响应满足您的需要，请将请求的模式设置为"no-cors"以在禁用CORS的情况下提取资源。
这是我的Program.cs代码：

var builder = WebApplication.CreateBuilder(args);

var connectionString = builder.Configuration.GetConnectionString("DefaultConnection");

builder.Services.AddTransient<BillEmailService>();
builder.Services.AddTransient<TransactionInfoService>();
builder.Services.AddTransient<PaymentProviderService>();
builder.Services.AddTransient<StoreInfoService>();
builder.Services.AddTransient<DbSetup>();

builder.Services.AddTransient<InlineImageService>();
builder.Services.AddHttpClient<InlineImageService>();

builder.Services.AddTransient<Feedback>();

builder.Services.AddTransient<LoyaltyEngineFactory>();
builder.Services.AddHttpClient("LoyaltyEngineFactory");

builder.Services.AddTransient<MasterpassClientFactory>();
builder.Services.AddHttpClient("MasterpassClient");

builder.Services.AddTransient<TransactionInfoFactory>();
builder.Services.AddHttpClient("TransactionInfoClient");

builder.Services.AddSingleton<IDbConnectionFactory>(s => new DbConnectionFactory(connectionString));
builder.Services.AddTransient<IDbAdapter, DbAdapter>();

builder.Services.AddControllers().AddJsonOptions(options =>

    options.JsonSerializerOptions.PropertyNamingPolicy = null);

builder.Services.AddSwaggerGen(c =>
{
    c.SwaggerDoc("v1", new OpenApiInfo { Title = "WebApp", Version = "v1" });
});

var app = builder.Build();

if (app.Environment.IsDevelopment())
{
    app.UseDeveloperExceptionPage();

}

app.UseSwagger();
app.UseSwaggerUI(c => c.SwaggerEndpoint("/swagger/v1/swagger.json", "WebApp v1"));

app.UseHttpsRedirection();

app.UseRouting();

app.UseAuthorization();
app.UseDefaultFiles();
app.UseStaticFiles();

app.MapControllerRoute("default", "{controller=Demo}/{action=Get}/{id?}");
app.MapFallbackToFile("index.html");


using var scope = app.Services.CreateScope();
var repo = scope.ServiceProvider.GetService<DbSetup>();
await repo!.RunScripts();

app.Run();

我该如何着手修复此错误？