You just have to use X509Certificates validator like this :-
using System.Net;
#if UNITY_EDITOR
public static bool Validator (object sender, System.Security.Cryptography.X509Certificates.X509Certificate certificate, System.Security.Cryptography.X509Certificates.X509Chain chain, System.Net.Security.SslPolicyErrors sslPolicyErrors)
         {return true;}
#endif
void Start ()
{
#if UNITY_EDITOR
   ServicePointManager.ServerCertificateValidationCallback = Validator;
#endif
ServiceAPI serviceAPI = new ServiceAPI("KEY1","KEY2");
}
	This is also mentioned in README of the SDK.
	Use #if tag as i used, otherwise it'll give error on device.
	If your issue still exists or any other query,  feel free to ask us.