Substitution parameter formats for returning call timestamps in ISO 8601 within a custom webhook’s request body.
Symptoms
The ISO 8601 date-time format option isn’t available in the Substitute Parameter picker.
Applies to: Custom webhooks, within the request body configuration.
Resolution
Use one of the following formats directly in your webhook’s request body (call_start_time_pst below is an example custom parameter name for the webhook):
"call_start_time_pst": "<call_start_time_webhook_utc.date_time_strftime('%Y-%m-%d')>" — returns a string like “2024-02-27.”start_time_utc.date_time_iso8601 — returns a string like “2024-02-27T09:36:58+00:00.”start_time_utc.date_time_iso8601_zulu — returns a string like “2024-02-27T09:36:58Z.”
Last modified on September 30, 2026
