What is auto top-up?

An optional card-on-file feature that refills your prepaid balance automatically when it runs low.

Optional. With a card on file, we automatically charge it for a fixed amount you choose (at least $10) whenever your prepaid balance reaches or drops below your low-balance threshold, so pay-as-you-go usage and any overflow you’ve enabled aren’t interrupted. You choose the amount and the threshold — the threshold has to sit below the amount so each top-up clears it — and you can turn it off anytime.

Good to know: it fires once each time your balance reaches or falls below the threshold, never in a loop, and skips the charge if a manual top-up already lifted the balance back up. After three declined charges in a row it switches itself off and emails you; fix the card, then re-enable it on the Billing page. Removing your saved card also turns it off.