Exception on the Httpresquest

Question

I am developing a login system for my app made in windows Forms. I created an API that works normally by Swagger, but when I try to request a request from my system for the API an error occurs. I reviewed the system code and saw that the error is not in it, as I can use other Apis (e.g., Viacep).

private static string urlApi = "http://localhost:5001           /WeatherForecast/teste?strTeste=teste";  

        HttpRequestMessage request = new HttpRequestMessage();
        

        private static async Task<string> TesteDeApi()
        {
            int teste = 0;

            try
            {

                HttpClient httpClient = new HttpClient();
                HttpResponseMessage res = await httpClient.GetAsync(urlApi);
                HttpContent content = res.Content;
                string data = await content.ReadAsStringAsync();

                MessageBox.Show(data);
            }
            catch(Exception e)
            {
                MessageBox.Show(e.ToString());
            }

            return teste.ToString();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            TesteDeApi();
        }

To make the request I use Httpclient. You could tell me why I made that mistake or how to fix it?