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

# fax.sending

> Sent when a delivery attempt against the destination begins.

## When it fires

At the start of each delivery attempt against the destination. A fax that retries on a transient failure will fire `fax.sending` again before the next attempt.

The current attempt is recorded in `attempts[]` with `started_at` set and `completed_at` null. Previous attempts (if any) are also present with their full detail.

## What your handler should do

* Use this for in-flight visibility - "fax is currently being sent."
* If you display fax status to your users, this is the event that moves the display from "queued" to "in progress."
* Do not finalize success or failure on this event. Wait for `fax.delivered` or `fax.failed`.

The number of `fax.sending` events for a single fax depends on how many delivery attempts run, which is bounded by `max_attempts` (1 to 5, default 3).


## OpenAPI

````yaml openapi.json webhook fax.sending
openapi: 3.1.0
info:
  title: mintfax API
  version: '1.0'
  description: >-
    Developer-first fax API. Send faxes with a single API call.


    ## Authentication


    Most endpoints require a Bearer token in the `Authorization` header.


    - **Account keys** (`mfx_acct_...`) access account-level endpoints
    (`/account`, `/account/balance`, `/account/transactions`, `/account/keys`).

    - **Environment keys** (`mfx_test_...` for test, `mfx_live_...` for live)
    access operational endpoints (`/environment`, `/faxes`, `/webhooks`,
    `/events`).

    - Registration endpoints (`POST /account/register` and `POST
    /account/register/verify`) do not require authentication.


    ## Base URL


    All API requests use `https://api.mintfax.com/v1` as the base URL.
  contact:
    name: mintfax Support
    email: support@mintfax.com
    url: https://mintfax.com/docs
servers:
  - url: https://api.mintfax.com/v1
    description: Production
security:
  - bearerAuth: []
tags:
  - name: Account
    description: >-
      Account-level resources: registration, account info, balances, and API
      keys.
  - name: Environment
    description: >-
      Test and live environment configuration shared across all operational
      requests.
  - name: Fax
    description: Send, list, retrieve, resend, and purge faxes.
  - name: Events
    description: >-
      Read the immutable event log for everything that has happened in the
      environment.
  - name: Webhooks
    description: >-
      Manage webhook endpoints and inspect or replay individual delivery
      attempts.
paths: {}
components:
  securitySchemes:
    bearerAuth:
      type: http
      description: |-
        API key as Bearer token. Use an account key (`mfx_acct_...`) for
        `/account/*` endpoints, and an environment key (`mfx_test_...` for
        sandbox, `mfx_live_...` for live) for `/environment/*`, `/faxes`,
        `/webhooks`, and `/events`.
      scheme: bearer

````