[Metronome official skills, corrections + diagnostics]: The checklist: event_type must exactly match a billable metric's event_type_filter (the #1 cause; the filter is immutable, so a wrong one means archiving the metric and creating a new one); events older than 34 days are silently dropped and unrecoverable; string numbers like "tokens": "1500" make SUM aggregation produce zero; and a missing or misspelled aggregation_key property does the same. Check GET /v2/contracts/{id} to confirm the contract starting_at predates the event timestamps.

Context: Usage events are ingested by Metronome but the invoice shows zero usage. Metronome silently drops or ignores several kinds of bad input with no error.