Error 400 when requesting access token to auth2

In C#, framwork 3.5, I'm requesting the access token to do things.
So I create a quick desktop app to test my class and everything works fine.
Then I move it to my web app, but when I run it i get Error 400 - Bad request.

I check and both calls are equal. What am I missing?

This is my code (i get the error ar (HttpWebResponse)request.GetResponse();):

        public static string getAccessToken(string clientId, string clientSecret, string tenantId)
        {

            var authority = string.Format("https://login.microsoftonline.com/{0}/oauth2/token", tenantId);
            var resource = "https://graph.microsoft.com";
            var postData = string.Format("grant_type=client_credentials&client_id={0}&client_secret={1}&resource={2}",clientId, clientSecret, resource);
            var request = (HttpWebRequest)WebRequest.Create(authority);

            request.Method = "POST";
            request.ContentType = "application/x-www-form-urlencoded";

            using (var streamWriter = new StreamWriter(request.GetRequestStream()))
            {
                streamWriter.Write(postData);
                streamWriter.Flush();
            }

            var response = (HttpWebResponse)request.GetResponse();
            var responseStream = response.GetResponseStream();
            var responseString = new StreamReader(responseStream).ReadToEnd();
                
   

            tokenResponse tResponse = JsonConvert.DeserializeObject<tokenResponse>(responseString);
            return tResponse.access_token;

        }

I check clientId, clientSecret and tenantId from Microsoft Graph and they are ok.

EDIT: I create a desktop application. If I run it from my client, it works. If I run from the server, I get the error. What should I check? Firewall is open, it is a Web server

This works:

public class tokenResponse
{
    public string resource { get; set; }
    public string token_type { get; set; }
    public int expires_in { get; set; }
    public int ext_expires_in { get; set; }
    public int expires_on { get; set; }
    public int not_before { get; set; }
    public string access_token { get; set; }
}

public static string getAccessToken(string clientId, string clientSecret, string tenantId)
{
	string grant_type = "client_credentials";
	string scope = "https://graph.microsoft.com/.default";
	
	var uri = string.Format("https://login.microsoftonline.com/{0}/oauth2/v2.0/token", tenantId);
	var postData = string.Format("client_id={0}&client_secret={1}&grant_type={2}&scope={3}", clientId, clientSecret, grant_type, scope);
	var request = (HttpWebRequest)WebRequest.Create(uri);

	request.Method = "POST";
	request.ContentType = "application/x-www-form-urlencoded";

	using (var streamWriter = new StreamWriter(request.GetRequestStream()))
	{
		streamWriter.Write(postData);
		streamWriter.Flush();
	}

	var response = (HttpWebResponse)request.GetResponse();
	var responseStream = response.GetResponseStream();
	var responseString = new StreamReader(responseStream).ReadToEnd();

	tokenResponse tResponse = JsonConvert.DeserializeObject<tokenResponse>(responseString);
	return tResponse.access_token;
}