Usage metering

Receive an identifiable event

Each usage event names the subscription, meter, external event identity, occurrence time, receipt time and quantity. Verify the authorised source before accepting it. The same source identity with the same payload returns the earlier result. The same identity with a changed payload is a conflict requiring investigation.

This protects the quantity when a producer retries after a timeout or two workers receive the same message. An accepted webhook does not establish a second billable event. Retain the original payload digest and provider context so an operator can explain why an event was accepted, rejected or identified as a duplicate.

Use the billing window consistently

The billing interval includes its start instant and excludes its end instant. An event at the end belongs to the next interval. Use the business occurrence time for allocation and the receipt cutoff to determine which accepted events were known to a particular billing candidate.

Late arrivals need a configured policy. They can enter a new unissued candidate or create a reviewed adjustment for an already issued interval. They must not silently change an issued invoice. The frozen aggregate retains the exact accepted event set, meter version, interval and cutoff that supplied its quantity.

Apply the meter’s aggregation method

Sum meters add accepted non-superseded quantities in the interval. Maximum meters select the largest qualifying measurement. Latest meters choose the last qualifying occurrence, using a stable event identity to break an equal-time tie. A meter change does not allow an old event to switch its meaning retrospectively.

For example, measurements of two, five and three produce ten under Sum, five under Maximum and three under Latest when the final measurement occurred last. The resulting quantity is only one part of pricing: the published plan separately applies included units, tier selection, base charges and the configured rounding rules.

Correct usage without erasing evidence

An erroneous event is corrected with a linked replacement under the authorised correction process. Preserve the earlier event and mark it superseded only when the replacement is accepted. A rejected correction leaves the existing accepted contribution unchanged. Cycles, cross-subscription replacements and repeated correction of a superseded branch are rejected.

If the event already contributed to an issued invoice, a correction produces a financial adjustment or credit review. It does not edit the prior invoice’s quantity in place. The customer and operator can see the original billed basis and the later correction that explains the changed charge.

Review the frozen aggregate

The Billing Manager reviews the candidate inputs before invoice issue. An aggregate that points to missing events, a conflicting provider receipt or a different subscription remains unresolved. A repeated billing worker reuses the same interval and source digest. It cannot bill the aggregate twice or swap in a different event set after approval. This gives the final invoice a traceable quantity instead of an unexplained counter that keeps changing after the customer receives it.