Hello,
the iOS client library underwent significant changes in the API with version 2.0, which was released in 2015. Those changes were needed to implement what we call "unified API", i.e. a common API for all our client libraries (iOS, Android, Java etc.).
A blog post from that time introduces the differences and shows how to convert your code:
blog.lightstreamer.com/2015/10/new-client-apis-for-ios-and-os-x.html.
Since then the iOS client has received significant additions, but only minor changes on existing API. Have a look at the blog post and feel free to ask if you need further help.
