asp.net core web api work on iis express but not working in iis on windows

i am new in asp.net core. i use asp.net core 2.1. i have two controller. a default valuecontroller that doesn't have db connection and customerController that have sqlserver db connection. when i run my project on iis express everything is good but when i publish my project and use windows iis value api work nice but my customer api that have a sqlserver connection doesn't work.

appsettings calss:

{
  "Logging": {
    "LogLevel": {
      "Default": "Warning"
    }
  },
  "AllowedHosts": "*",
  "ConnectionStrings": {
    "DefaultConnection": "Data Source=AHAD;Initial Catalog=mydb;Integrated Security=True"
  }
}

Startup class:

namespace SalesApp
{
    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.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);
            services.AddDbContext<MyDbContext>(Options =>
            {
                Options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection"));
            });
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IHostingEnvironment env)
            //,
    //ILoggerFactory loggerFactory,
    //MyDbContext db)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            else
            {
                app.UseHsts();
            }

            app.UseHttpsRedirection();
            app.UseMvc();
            //loggerFactory.AddConsole(Configuration.GetSection("Logging"));
            //loggerFactory.AddDebug();

            //db.Database.Migrate();

            //app.UseMvc();
        }
    }
}

MyDbContext class:

public class MyDbContext : DbContext
    {

        public MyDbContext()
        {

        }

        public MyDbContext(DbContextOptions<MyDbContext> options)
            : base(options)
        {

        }

        //public DbSet<CUSTOMER> customers { get; set; }

        public DbSet<CUSTOMER> Customer { get; set; }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.Entity<CUSTOMER>(entity =>
            {
                entity.Property(e => e.C_Code).HasMaxLength(5);
                entity.Property(e => e.C_Name).HasMaxLength(60);
                entity.Property(e => e.C_Code_C).HasMaxLength(12);
            });
        }

    }

CustomerController Class:

[Route("api/[controller]")]
    [ApiController]
    public class CustomerController : ControllerBase
    {
        MyDbContext _context;

        public CustomerController(MyDbContext context)
        {
            _context = context;
        }

        [HttpGet]
        public IActionResult GetCustomers()
        {
            return new ObjectResult(_context.Customer);
        }

    }

values api: enter image description here

customer api: enter image description here

it confused me 2 weeks.