Issue

Events sent to Segment fail to ingest and are not visible in the destination or logs. The error message "id_not_string: The userID or anonymousID was an empty string or not a string" appears, and sample payloads for these failed events are unavailable.

Product

Segment

Environment

Segment Console

Cause

Segment requires every event to include either a userId or anonymousId for successful ingestion. If both identifiers are missing or empty, the event does not meet ingestion criteria and is immediately discarded. No logs or metadata are stored for these dropped events.

Resolution

Ensure that every event sent to Segment includes at least one of the following identifiers: userId or anonymousId. Add validation checks in your instrumentation to confirm these fields are present before sending events. Including an event name is also recommended for successful processing.