---
title: "Fax Sending Started"
method: POST
path: "fax.sending.started"
tags: ["Callbacks"]
---

# Fax Sending Started

`POST fax.sending.started` (webhook)

This webhook uses Telnyx headers (telnyx-timestamp, telnyx-signature-ed25519) that are compatible with Standard Webhooks specification for SDK generation. Custom validation logic can map these to standard webhook-timestamp and webhook-signature equivalents. See https://github.com/standard-webhooks/standard-webhooks for details.

## Headers

- `telnyx-timestamp` integer, required — Unix timestamp for replay attack prevention
- `telnyx-signature-ed25519` string, required — Ed25519 signature of timestamp|payload for verification

## Payload

- FaxSendingStarted
  - `data` object
    - `record_type` 'event' — Identifies the type of the resource.
    - `id` string, uuid — Identifies the type of resource.
    - `occurred_at` string, date-time — ISO 8601 datetime of when the event occurred.
    - `event_type` 'fax.sending.started' — The type of event being delivered.
    - `payload` object
      - `connection_id` string — The ID of the connection used to send the fax.
      - `direction` 'inbound' | 'outbound' — The direction of the fax.
      - `fax_id` string, uuid — Identifies the fax.
      - `original_media_url` string — The original URL to the PDF used for the fax's media. If media_name was supplied, this is omitted
      - `media_name` string — The media_name used for the fax's media. Must point to a file previously uploaded to api.telnyx.com/v2/media by the same user/organization. Supported formats: PDF, TIFF, JPEG, PNG, DOC, DOCX, RTF, and TXT. media_name and media_url/contents can't be submitted together.
      - `to` string — The phone number, in E.164 format, the fax will be sent to or SIP URI
      - `from` string — The phone number, in E.164 format, the fax will be sent from.
      - `user_id` string, uuid — Identifier of the user to whom the fax belongs
      - `status` 'sending' — The status of the fax.
      - `client_state` string — State received from a command.
  - `meta` object — Metadata about the webhook delivery.
    - `attempt` integer — The delivery attempt number.
    - `delivered_to` string, uri — The URL the webhook was delivered to.

## Acknowledgement `200`

The server must return an HTTP 200, otherwise we will reattempt delivery at the failover webhook URL.

---

[API](https://skmtc.net/team-telnyx/apis/telnyx-api-2.md) · [All operations](https://skmtc.net/team-telnyx/apis/telnyx-api-2/llms.txt) · [OpenAPI document](https://skmtc-service-staging.skmtc.workers.dev/v1/apis/team-telnyx/telnyx-api-2/versions/8f5f4e537994/schema)