[billing-doctor docs]: TIMESTAMP_INVALID means the timestamp field is malformed; check the ISO 8601 format and valid date values. DUPLICATE_TRANSACTION_ID is the dedup guard firing: when unique_id matching is on, resending an event with the same unique_id produces a new error object but is not a duplicate event, so use genuinely unique IDs per event or batch idempotent events in one call. AGGREGATION_KEY_INVALID means the aggregation_key is not a valid property or group_by key for the billable metric, so confirm the key exists in the metric definition. TIMESTAMP_OUT_OF_BOUNDS marks data outside the 34-day backdating window.

Context: Three billing-doctor errors that map to specific event-payload defects.

## Matched source
Source: Source: https://github.com/thedaviddias/billing-doctor/blob/HEAD/docs/metronome/errors.md
Original query: "Metronome billing-doctor error codes: timestamp, duplicate transaction, bad aggregation key"
Key terms: aggregation, billing, codes, doctor, duplicate, error, metronome, timestamp, transaction