Heya there. Sorry I probably can't help much, but I have it working well for Android, and from what I've read in the Manual etc, the same plugin and setup is used for iOS.
Here are snippets of what I have that may help you out. This is all that is needed if you want a 'remove ads' button functioning in Android (assuming its the same for iOS). You can ignore the other stuff
NOTE: "remove_adverts" & "currency_1" etc are items I had to create in the Google Developer Console, so you'll need to do the equivalent for Apples Developer site (which I haven't tried yet).