Chartboost 5.0 plugin ios intergration

I am trying to set up chartboost in my app(first unity app). I am using 5.0 plugin. I have set up the appid bit and i have called showInterstitial(CBLocation.Default);, it is not showing any ads. In the debugger in xcode it says "The Chartboost SDK needs to be initialized before we can show any ads". Does anyone know where to initalize it with the new plugin? it seems that it can no longer be done with CBBindings. Many thank for your help