Add to Lync contact list by UCMA 4.0

I am using UCMA 4.0 for developing a lync bot. I simply wrote some codes for adding a contact:

UCMASampleHelper helper = new UCMASampleHelper();
UserEndpoint userEndPoint = helper.CreateEstablishedUserEndpoint("Hello_World_User");
string targetURI = "sip:u2@lync.local";

userEndPoint.ContactGroupServices.EndSubscribe(userEndPoint.ContactGroupServices.BeginSubscribe(null, null));
userEndPoint.ContactGroupServices.EndAddContact(userEndPoint.ContactGroupServices.BeginAddContact(targetURI, null, null));

helper.ShutdownPlatform();

But after running the execution file, the contact is not shown in the list by signing into Lync client. Do I miss any steps?