The account's monthly overage budget

The most metered overage may cost this account per period, in USD cents. 0 means NO overage: the plan caps refuse exactly as they would without overage billing. Enforcement hard-stops new overage at this number and invoicing never exceeds it, so it is a real spend ceiling, not an alert threshold.

Readable on every plan (free and enterprise simply read 0 and cannot set one — see the PUT).