ASP .NET Core Web API + Android kotlin App

I've made a ASP.NET Core Web API (hosted locally IIS Express) and I'm trying to get data from it from my Android app (kotlin), but I always get a "Bad request" or "FileNotFoundException" (depending on which method of getting the data is used). I know I can successfully retrieve data from other web API's, but not for mine.

I also tried googling my problem but with no luck on finding the answer.

Retrieving data from my Web API works from browser (http://localhost:24517/bar?username=smthg&password=smthg)

My C# controller:

[HttpGet]
        [Route("[controller]")]
        public Bar Authenticate(string username, string password)
        {
            Bar bar = new Bar();
            try
            {
                var user = context.Users.FirstOrDefault(u => u.Username == username && u.Password == password);

                bar = context.Bars.
                    Include(b => b.Inventory).
                    ThenInclude(i => i.Items).
                    Include(b => b.Users.Where(u => u.Id == user.Id)).
                    ToList().
                    Find(b => b.Users.ToList().Find(u => u.Id == user.Id) == user);
            }
            catch (Exception)
            {
                
            }


            return bar;
        }

My kotlin request:

const val URL = "http://192.168.0.13:24517/bar"
const val USERNAME = "username=";
const val PASSWORD = "password=";

class BarRepo : IRepoBar {

    override fun getBarByUserAsync(userName: String, password: String): Bar {
        val url = "$URL$USERNAME$userName&$PASSWORD$password"

        val apiResponse = URL(url).readText()



        val obj = Json.decodeFromString<Bar>(apiResponse)
        return obj
    }
}