Error : That assembly does not allow partially trusted callers

Hi,,

I have D365 online , and I created a plugin that having a service to send SMS messages.

That service it's out side source, I added to the project as service reference  (Visual Studio 'C#').

The code giving me the error is :-

 SMS.SMSIntegration webserviceSendMsg = new SMS.SMSIntegration();

when I'm trying to create an object from that class to send the SMS message, the D365 giving me this error :-

Your help in this regard will be highly appreciated!

Thanks ..