List requests async ingestion accepted but could not apply

Newest first. Only populated for apps that ingest asynchronously (INGEST_ASYNC_MODE): a 202 there means durably accepted, and an item that later fails for good is dead-lettered here instead of reaching the caller. reason_code is derived_event_code (the event code is computed by the platform), contact_change_requires_server_key (a publishable key tried to replace an email or phone; only the offending event, or the whole identify call, is dropped), data_error (the database refuses a value of the event or identify call on every attempt, e.g. an external id too large to index; message names only the SQLSTATE and the column or constraint), invalid_payload, or max_attempts_exceeded. Payloads (properties, traits, channel addresses) are never returned. Kept for 30 days.