Why a completed import is partial. RECORDS_FAILED means some records were not imported (see failedRecords). SELECT_OPTION_LIMIT_REACHED means people were imported but new select option values were left off because the property is at its option limit (see warnings). Empty when the import fully succeeded, is still running, or failed.
Response
Success
Changes
Webhooks have no change history: a webhook is keyed by its event name rather than a path and method, so no recorded change can name it.