I know it feels like overkill, but I’d recommend either outsourcing (even Stripe has usage-based billing if you can keep your updates under 100/s) or using something off-the-shelf like https://killbill.io.
I know it seems like a simple problem, but billing systems quickly turn into Eldridge horrors, even if you have the best intentions, and it’s always nicer to have someone else to maintain that for you.
I know it seems like a simple problem, but billing systems quickly turn into Eldridge horrors, even if you have the best intentions, and it’s always nicer to have someone else to maintain that for you.