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I´m trying to send a email using Oauth2, but i´m getting a error when i authenticate my user. This is the error "An unhandled exception of type 'MailKit.Security.AuthenticationException' occurred in mscorlib.dll

Additional information: 334: eyJzdGF0dXMiOiI0MDAiLCJzY2hlbWVzIjoiQmVhcmVyIiwic2NvcGUiOiJodHRwczovL21haWwuZ29vZ2xlLmNvbS8ifQ== "

Here's my code:
C#
using (var stream = new FileStream("credentials.json", FileMode.Open, FileAccess.Read))
            {
                string credPath = "token.json";
                credential = GoogleWebAuthorizationBroker.AuthorizeAsync(
                    GoogleClientSecrets.Load(stream).Secrets,
                    Scopes,
                    "user@gmail.com",
                    CancellationToken.None,
                    new FileDataStore(credPath, true)).Result;
                Console.WriteLine("Credential file saved to: " + credPath);
            }
            var service = new GmailService(new BaseClientService.Initializer()
            {
                HttpClientInitializer = credential,
                ApplicationName = ApplicationName,
            });
 var message = new MimeMessage();
            message.From.Add(new MailboxAddress("User", "user@gmail.com"));
            message.To.Add(new MailboxAddress("Test", "test@gmail.com"));
            message.Subject = "Test";
            message.Body = new TextPart("plain")
            {
                Text = "Test"
            };
            
            using (var client = new MailKit.Net.Smtp.SmtpClient())
            {
                client.Connect("smtp.gmail.com", 587);
                // use the access token 
                var oauth2 = new MailKit.Security.SaslMechanismOAuth2(credential.UserId, credential.Token.AccessToken);
                client.Authenticate(oauth2);
                client.Send(message);
                client.Disconnect(true);
            }


What I have tried:

I tried activating the gmail's "less security options", but still doesn't work
Posted
Updated 20-May-20 4:15am

The 334 indicates an authentication error of some kind - I'd have expected extra information in the response alluding to the exact problem
 
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I would recommend that you read through the following page and verify that you have everything set up correctly; sounds like the MailKit sample code may not be the same as Google provides
MailKit Issue #962: AuthenticationException 334[^]

It also told you how to decode the Additional Information, which is just Base64
Base64.Decode(Additional Info)
{"status":"400","schemes":"Bearer","scope":"https://mail.google.com/"}
 
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