Cool post! I don't have a ton of experience using Stripe, but shouldn't you at least be handling some sort of payment_failed webhook?

It looks like you call _createSubscription and set the initial value for currentPeriodEnds before you know the payment actually succeeded, and since you don't ever check or listen for failed payments, anyone could get a free month (or year) of Checkly by using a bad card, or if the payment just randomly fails.

Maybe this isn't a huge deal in the early days, but you and your customer might not even notice the failed payment for quite a while unless you happen to check your Stripe dashboard!