NOTE:
There seems to be a SERIOUS problem with monthly AppleCare+ payments.
To automatically pay the $9.99 every month the AppleCare+ plan needs to be linked to an iTunes account, but the website Apple has to do this is broken. I’m on my third payment for my XS and this still isn’t fixed, after over a month talking to an Apple supervisor on the phone and getting the case escalated and escalated. Last I heard was 3 days ago, nothing had changed.
You can still do it, but you will need to remember to pay it yourself every month by going to the website and entering your card, if you forget or wait too long to pay it you will become ineligible for coverage.
I don’t have a clue how widespread this issue is, but from what I’ve been told it’s a common problem.