Bad Request - OAuth Access Token Generation

I have created server to server OAuth App in marketplace
My code like below
string encodedCredentials = Convert.ToBase64String(Encoding.UTF8.GetBytes($“{clientId}:{clientSecret}”));

// Set up API request header
var requestHeaders = new
ContentType = “application/x-www-form-urlencoded”,
Authorization = $“Basic {encodedCredentials}”

// Set up the body of the access token request
var requestBody = new
grant_type = “account_credentials”,
account_id = accountId

// Convert request body to URL-encoded form data
string requestBodyString = string.Join(“&”, requestBody.GetType().GetProperties()
.Select(property => $“{Uri.EscapeDataString(property.Name)}={Uri.EscapeDataString(property.GetValue(requestBody)?.ToString())}”));

// Send the POST request to the token API
using (var httpClient = new HttpClient())
var requestContent = new StringContent(requestBodyString, Encoding.UTF8, “application/x-www-form-urlencoded”);

var response = await httpClient.PostAsync("", requestContent);

if (response.IsSuccessStatusCode)
	// Parse and use the access token from the response
	string jsonResponse = await response.Content.ReadAsStringAsync();
	Console.WriteLine($"Access Token: {jsonResponse}");

but getting Bad request in response
My Plan is basic plan

Can you follow this blog: Troubleshooting Server-to-Server Oauth access tokens to troubleshoot the error?