Asp.net – Can't access my API for SQL Server (Error 500)

I am hosting a site on IIS (Windows Server 2022), and trying to implement a simple register-login system via simple ASP.Net Core Web API, but while I can manipulate database internally, I cannot do it externally, nor via the curl test commands.

In the event logs there is an error "Reason: Could not find a login matching the name provided.", but the login is correct, when I try to run cmd sqlcmd -S <my domain> -d UsersDatabase -U <userlogin> -P <password> -Q "SELECT * FROM users;" – it works perfectly, so credentials seem to be working.

I tried to log extensively but no logs are even created, the code does not runs it seems?
Do I miss something stupid, did I deploy the app itself wrong, missed additional allowance for external requests or something?

Here is my current class of the API:

using System;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc;
using Microsoft.EntityFrameworkCore;
using BCrypt.Net;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Logging;
using Serilog.Core;

namespace APIInjector
{
    public class User
    {
        public int Id { get; set; }
        public string? Login { get; set; }
        public string? Nickname { get; set; }
        public string? PasswordHash { get; set; }
        public string? Email { get; set; }
        public bool EmailConfirmed { get; set; }
    }

    public class UserInputModel
    {
        public string? Login { get; set; }
        public string? Password { get; set; }

    }

    public class UsersDbContext : DbContext
    {
        public UsersDbContext(DbContextOptions<UsersDbContext> options) : base(options)
        {
        }

        public DbSet<User>? Users { get; set; }
    }

    [ApiController]
    [Route("api/users")]
    public class UsersController : ControllerBase
    {
        private readonly UsersDbContext _dbContext;
        private readonly ILogger<UsersController> _logger;

        public UsersController(UsersDbContext dbContext, ILogger<UsersController> logger)
        {
            _dbContext = dbContext;
            _logger = logger;
        }

        [HttpPost("register")]
        public async Task<IActionResult> Register(UserInputModel userInput)
        {
            _logger.LogInformation("Register action was called");

            if (await _dbContext.Users!.AnyAsync(x => x.Login == userInput.Login))
            {
                return BadRequest("User already exists");
            }

            var user = new User
            {
                Login = userInput.Login,
                PasswordHash = BCrypt.Net.BCrypt.HashPassword(userInput.Password),

            };

            _dbContext.Users!.Add(user);
            await _dbContext.SaveChangesAsync();

            return Ok(new { Message = "User registered successfully" });
        }

        [HttpPost("login")]
        public IActionResult Login(UserInputModel userInput)
        {
            _logger.LogInformation("Login action was called");

            var existingUser = _dbContext.Users!.FirstOrDefault(u => u.Login == userInput.Login);

            if (existingUser == null || !BCrypt.Net.BCrypt.Verify(userInput.Password, existingUser.PasswordHash))
            {
                return Unauthorized(new { Message = "Invalid login credentials" });
            }


            return Ok(new { Message = "Login successful" });
        }
    }
    public class Startup
    {

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

        public IConfiguration Configuration { get; }

        public void ConfigureServices(IServiceCollection services)
        {

            services.AddDbContext<UsersDbContext>(options =>
                options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));

            services.AddControllers();
        }

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

            app.UseRouting();

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

}

Appsettings.json:

{
  "ConnectionStrings": {
    "DefaultConnection": "Server=<domain>;Database=UsersDatabase;User Id=<username>;Password=<password>"
  },
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft.AspNetCore": "Warning"
    }
  },
  "AllowedHosts": "*"
}

Program.cs:

using APIInjector;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using Serilog;
using System;

public class Program
{
    public static void Main(string[] args)
    {
        Log.Logger = new LoggerConfiguration()
            .WriteTo.File("E:\logs\myapp.txt")
            .CreateLogger();

        try
        {
            var host = CreateHostBuilder(args).Build();
            host.Run();
        }
        catch (Exception ex)
        {
            Log.Fatal(ex, "Host terminated unexpectedly");
            Console.WriteLine("Press any key to close the application...");
            Console.ReadKey();
        }
        finally
        {
            Log.CloseAndFlush();
        }
    }

    public static IHostBuilder CreateHostBuilder(string[] args) =>
        Host.CreateDefaultBuilder(args)
            .UseSerilog() 
            .ConfigureWebHostDefaults(webBuilder =>
            {
                webBuilder.UseStartup<Startup>();
            });
}

Tried to log, as can be seen, but it just shows that program starts and listens.

curl -X POST -H "Content-Type: application/json" -d '{"Login":"testuser","Password":"testpassword"}' https://<domain>/APIInjector/api/users/register

returns just error 500 without any details, with that login error in the event logs server-side