我正在尝试进行API调用;我启动Visual Studio并在postman中输入以下内容：

http://localhost:51266/api/country

我在方法上设置了一个断点，但什么也没发生。404找不到了
这是控制器：

[Route("api/[controller]")]
[ApiController]
public class CountryController : Controller
{
    private ICountryRepository countryRepository;

    public CountryController(ICountryRepository repository)
    {
        this.countryRepository = repository;
    }

    [HttpGet]
    public IActionResult GetCountries()
    {
        var countries = countryRepository.GetCountries().ToList();

        return Ok(countries);
    }
}

我做错了什么？
我在Startup中有这个：

public void ConfigureServices(IServiceCollection services)
{
    services.AddMvc();

    var connectionString = Configuration["connectionStrings:bookDbConnectionString"];
    services.AddDbContext<BookDbContext>(c => c.UseSqlServer(connectionString));

    services.AddScoped<ICountryRepository, CountryRepository>();
}

我现在是这样的：

[ApiController]
public class CountryController : Controller
{
    private ICountryRepository countryRepository;

    public CountryController(ICountryRepository repository)
    {
        this.countryRepository = repository;
    }

    [HttpGet]
    [Route("api/[controller]")]
    public IActionResult GetCountries()
    {
        var countries = countryRepository.GetCountries().ToList();

        return Ok(countries);
    }
}

我的startup class：

public class Startup
{
    public static IConfiguration Configuration { get; set; }

    public Startup(IConfiguration configuration)
    {
        Configuration = configuration;
    }

    // This method gets called by the runtime. Use this method to add services to the container.
    // For more information on how to configure your application, visit https://go.microsoft.com/fwlink/?LinkID=398940
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddMvc();

        var connectionString = Configuration["connectionStrings:bookDbConnectionString"];
        services.AddDbContext<BookDbContext>(c => c.UseSqlServer(connectionString));

        services.AddScoped<ICountryRepository, CountryRepository>();
    }

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

        app.UseRouting();
    }
}

如果我这样做：

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

        //app.UseRouting();

        app.UseMvc();
}

我得到了这样的警告：
警告MVC 1005
在使用端点路由时，不支持使用“JumeMvc”配置MVC。若要继续使用“MvcOptions.EnableEndpointRouting = false”，请在“ConfigureServices”中设置“MvcOptions.EnableEndpointRouting = false”。WebApplication2 D：\Mijn Documents\VisualStudio_2019\WebApplication2\WebApplication2\Startup.cs