Usage-based billing requires clear billable-event definitions, stable event IDs, deduplication, correction policies, and reconciliation. Fast quota counters can be approximate, while invoicing requires durable auditable records; do not treat a cache counter as financial evidence.

Audit logs should capture actor, tenant, timestamp, target, action, and outcome for privileged changes. Protect logs against unauthorized modification and define retention. Support tooling should enforce tenant boundaries and record cross-tenant access.

Reconcile raw usage, aggregates, and billed totals periodically. Late or duplicated events should be corrected through an auditable process rather than silent manual edits.