I am consuming an API with basic Authentication oauth and returns: Incorrect request (400)

Question

Talk, you guys!

Next, I developed an api in spring boot and already tested with Postman and it works normally, its security is a very basic oauth authentication. Now I’m testing in an application in c# I have here to return the token to be able to consume the endpoints, however when I’m making the call to return the token is returning me:

"System.Net.WebException: 'O servidor remoto retornou um erro: (400) Solicitação Incorreta.'"

Follow the code below:

        WebRequest req = WebRequest.Create(@"http://localhost:8080/oauth/token");
        req.Method = "POST";

        req.Headers["Authorization"] = "Basic " + Convert.ToBase64String(Encoding.Default.GetBytes("apisustentacao:HHednf8iwFgre$$$@"));
        HttpWebResponse resp = req.GetResponse() as HttpWebResponse;

In Postman this working normally:

Below is more picture of the Postman header:

I appreciate anyone who can help me