What happens to usage events sent after the grace period ends

Events sent after a billing period's grace period has closed can't be applied to that period's invoice. Once the grace period ends and the invoice is finalized, the billing period's charge boundaries are locked. Late events are still accepted by the API, but they won't appear on any invoice, past or future, because each invoice only queries events whose timestamps fall within its own specific charge boundaries.

How it works

Lago sets a charges_from_datetime and charges_to_datetime for every billing period. While an invoice is in draft, during the grace period, it can be refreshed and will pick up late-arriving events whose timestamps fall within those boundaries. Once the invoice is finalized, those boundaries are closed, and no further event ingestion affects it. An event timestamped inside a finalized period simply isn't counted on any invoice.

How to confirm the cause

Check the event's timestamp field against the finalized invoice's charges_to_datetime. If the event falls within a period whose invoice is already finalized, it wasn't counted on that invoice and won't appear on any future invoice automatically.

What to do

There are two practical options: create a one-off invoice to bill for the missed usage (fees must be specified manually, since one-off invoices don't re-query events), or accept that the usage can't be recovered automatically and communicate that to the customer. Voiding and regenerating the original invoice won't help, the regenerated invoice is built from the voided invoice's fee data, not by re-querying events, so late events are still excluded.

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