Please try ignoring/bypass the SSL certificate and share your feedback with us if it resolves your problem.
Sample Code:
// Register callback method for SSL validation event
ServicePointManager.ServerCertificateValidationCallback += RemoteCertificateValidationHandler;
// This event handler is called when SSL certificate is verified
private static bool RemoteCertificateValidationHandler(object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors)
{
return true; //Ignore the checks and go ahead
}