Postpaid auto-charge and low-balance modal

v0.5.5.0 closes the gap between “your balance is low” and “we silently stopped your service.” Customers with a card on file are charged proactively when balance dips below the threshold. Customers without a card see a modal asking them to add one before anything fails. The number-fee tick continues to debit balance at the 30-day mark, and postpaid auto-charge then settles any negative balance against the card on file.

What changed

• Auto-charge cron runs on a regular cadence and tops the balance back up when it falls below the threshold and a default payment method is on file. The charge uses the existing Stripe PaymentIntent path against the saved card.
• Low-balance modal shows once per browser session when balance is under $2 and either no card is on file, or a recent usage event was blocked. Two variants:
  • No card on file: “Add a payment method to keep your number active.” Primary CTA opens Stripe-hosted Setup Checkout.
  • Charge failed: “We couldn’t charge your card.” Primary CTA goes to /billing for a payment-method update.
• Suspension reinstate webhook restores service automatically once a card update succeeds, with no support ticket needed.
• Number-fee mechanics unchanged. The $2.50/month per-number fee still debits balance at the 30-day mark. The difference: when balance goes negative, postpaid auto-charge picks it up instead of the line being suspended in limbo.

Trigger conditions

The modal triggers on balance < $2 AND (no card on file OR recent blocked-usage signal within 24h). Blocked-usage covers both failed calls rows and the pre-call / pre-SMS reject events (call_rejected_insufficient, sms_rejected_suspended, and so on). This catches the painful failure mode where the API rejected a 402 before any call record was written.

What you need to do

Nothing. If you have a card on file, auto-charge is already running. If you don’t, you’ll see the modal next time your balance dips below threshold. Add a card to dismiss it for good.