> ## Documentation Index
> Fetch the complete documentation index at: https://docs.invoca.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Standardizing Timestamps in Custom Webhooks to ISO 8601 DateTime Format

> 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."

## Where to go next

* [How to Create, Edit, or Clone an Invoca Webhook](/s/article/create-edit-clone-invoca-webhook)
* [Integration Troubleshooting](/s/article/integration-troubleshooting)