How to bypass invalid SSL certificate.
You can bypass the certificate check, and solve this error, by override the certificate check on the callback function on the HttpClientHandler
like the below code.
HttpClientHandler clientHandler = new HttpClientHandler();
clientHandler.ServerCertificateCustomValidationCallback = (sender, cert, chain, sslPolicyErrors) => { return true; };
using(var httpClient = new HttpClient(clientHandler))
{
// your code
}