How to correct a usage event that was sent with the wrong value

You can't delete or edit an event once it's been sent to Lago. How you correct a wrong value depends on the billable metric's aggregation type, and for some types there's no reliable self-service fix at all.

How it works by aggregation type

Sum and weighted_sum. These add up event property values across the billing period, so you can correct an over-reported event by sending a new event with a negative value equal to the excess. The original event stays in the system, but the net result is corrected. This only works for pay-in-arrears billing. Pay-in-advance billing bases the fee on the maximum running total seen during the period, not the current sum, so a corrective event updates the running total in current usage but doesn't lower the previous maximum, producing a $0 fee and leaving the amount already billed unchanged.

Count_unique. Don't send a negative value. Send a corrective event with operation_type: "remove" in the event properties, alongside the property value to remove, which decrements the unique count by one.

Count, max, and latest. Negative correction events aren't a reliable strategy here. Count counts events regardless of property values, so a corrective event still increments the count. Latest floors negative values to 0, so a corrective event of -30 after a value of 100 changes the result to 0, not 70, replacing the original error with a more disruptive one. Max simply ignores a negative event, since max(100, -30) is still 100, so the correction does nothing and the billing stays wrong. For these three types, contact Lago support.

How to confirm the cause

Review the ingested events via GET /api/v1/events or the activity log to confirm the incorrect value that was sent, and identify the billable metric's aggregation type before choosing a correction strategy.

What to do (sum, pay-in-arrears)

Send a new event with the same code as the original, setting the relevant property to a negative number equal to the excess. For example, if units: 100 was sent by mistake and the correct value is 70, send a corrective event with units: -30, then verify the corrected usage in the customer's current usage view.

This article reflects guidance drawn from customer case resolutions. It is not officially supported documentation and may not apply to all situations.