Users who cancel in Stripe still have Pro in my app

checkout.session.completed fires once, at the start. For ongoing state you want the subscription events. The pattern that doesn't break:

Listen to:

• customer.subscription.created
• customer.subscription.updated (plan change, cancel scheduled, past_due, renewal period moves)
• customer.subscription.deleted (actually ended)
• invoice.payment_failed (optional, for sending a "fix your card" email)

In every one of them, do the same thing: fetch the subscription and write its current state. Don't try to compute state from the event type.

case "customer.subscription.created":
case "customer.subscription.updated":
case "customer.subscription.deleted": {
  const sub = event.data.object as Stripe.Subscription;
  await supabaseAdmin.from("subscriptions").upsert({
    id: sub.id,
    customer_id: sub.customer as string,
    status: sub.status,              // active, trialing, past_due, canceled, unpaid...
    price_id: sub.items.data[0].price.id,
    cancel_at_period_end: sub.cancel_at_period_end,
    current_period_end: new Date(sub.items.data[0].current_period_end * 1000).toISOString(),
  });
  break;
}

Then "is this user Pro" becomes: status in ('active','trialing') (decide yourself if past_due still gets access during retries).

Why your cancel didn't work: the portal by default cancels at period end. That sends customer.subscription.updated with cancel_at_period_end: true, and only when the period is over does customer.subscription.deleted arrive. So those users will lose Pro, just a month later. That's correct behavior, they paid for the month.

Note: on API versions from 2025-03-31 on, current_period_end lives on the subscription item, not the subscription. Older tutorials read sub.current_period_end, which is undefined on new accounts.