How to update user property after subscribing

hi,
I a few subscription apps.
Every week, users get charged and I need to add e.g. +2 credits into their account.

If they were to stop paying/unsubscribe, I’d need to update their user from Paying subscriber = true to False.

What do you recommend to use to implement this? (would the API be easy to duplicate if I make more subscription apps? or should I make a UPDATE request)