I’ve not gotten that far. I only saw CPC options in the videos and tutorials that I looked through. Our engineer said it should be called as soon as possible in your main.lua. Either as part of main.lua or as part of the applicationStarted system event. This seems to match where in the iOS delegate that they want it to happen.
Facebook has to understand that your apps will be installed from other places and it would be very unfair for them to charge you for apps people installed outside of Facebook. I don’t know if there is a forum or place to ask that question of Facebook, but how they operate is way beyond our ability to answer that.
Maybe you could search for publishinstall to find the other threads where people have been trying to get it going and PM some of those posters to see what their experience is.