Establish trust relationship for the SSL/TLS secure channel

Fix bugs:
#15 - Could not create SSL/TLS secure channel.
#16 - Object reference not set to an instance of an object

I fixed this error by adding this line before calling the web method:

System.Net.ServicePointManager.ServerCertificateValidationCallback = (senderX, certificate, chain, sslPolicyErrors) => { return true; };