Set, change, or turn off the automatic top-up rule [admin or billing role]

Set, change, or turn off the automatic top-up rule (admin or billing role): when the available balance falls below threshold_usd, the card on file is charged amount_usd (defaults: below $20, add $100). It is what keeps a prepaid organization running unattended - at zero compute stops and every disk is kept, and the rule buys the credit before that. Bounds: threshold $1 to $10,000, amount $10 to $10,000, whole cents; the rule runs at most 25 times per rolling 24 hours, within daily_limit_usd when you set one (0 clears it) and the platform's daily ceiling. A card must be on file: with none, buy_credits(amount_usd) answers with a payment link, and that one payment adds credit and saves the card. disable: true turns the rule off. Audited as a standing authorization to charge the card.