Client is unauthorized to retrieve access tokens using this method

[hakanak]

Hello,
I have a problem like this:

Error Line: 83

An unhandled exception of type 'Google.Apis.Auth.OAuth2.Responses.TokenResponseException' occurred in Google.Apis.dll

Additional information: Error:"unauthorized_client", Description:"Client is unauthorized to retrieve access tokens using this method.", Uri:""

Code:
` //UserCredential credential;
Dictionary<string, string> dictionary = new Dictionary<string, string>();
String serviceAccountEmail =
"[email protected]";

        var certificate = new X509Certificate2(@"key.p12", "notasecret", X509KeyStorageFlags.Exportable);


        ServiceAccountCredential credential = new ServiceAccountCredential(
            new ServiceAccountCredential.Initializer(serviceAccountEmail)
            {
                
                User = "[email protected]",
                AccessMethod = new BearerToken.AuthorizationHeaderAccessMethod(),
                DefaultExponentialBackOffPolicy = Google.Apis.Http.ExponentialBackOffPolicy.UnsuccessfulResponse503,
                
                Scopes = new[] { GmailService.Scope.MailGoogleCom }
            }.FromCertificate(certificate)
        );


            // Create Gmail API service.
            var gmailService = new GmailService(new BaseClientService.Initializer()
            {
                HttpClientInitializer = credential,
                ApplicationName = "MyApp",
            });

            // Define parameters of request.

            var emailListRequest = gmailService.Users.Messages.List("[email protected]");
            emailListRequest.LabelIds = "INBOX";
            emailListRequest.IncludeSpamTrash = true;
            emailListRequest.Q = "is:unread";
            emailListRequest.MaxResults = 10;

            var emailListResponse = emailListRequest.Execute();


            foreach (var item in emailListResponse.Messages)
            {
                Console.WriteLine(item.Id);
            }


        Console.Read();`

[erickoledadevrel]

It looks like you are using the .NET client library, which is supported here:

https://developers.google.com/api-client-library/dotnet/support