<!-- Auto-generated from Telnyx OpenAPI specs. Do not edit. -->

Telnyx Fax - JavaScript

Installation

npm install [email protected]

Setup

import Telnyx from 'telnyx';

const client = new Telnyx({
  apiKey: process.env['TELNYX_API_KEY'], // This is the default and can be omitted
  publicKey: process.env['TELNYX_PUBLIC_KEY'], // Required for client.webhooks.unwrap() (webhook verification)
});

All examples below assume client is already initialized as shown above.

Error Handling

All API calls can fail with network errors, rate limits (429), validation errors (422), or authentication errors (401). Always handle errors in production code:

try {
  const result = await client.messages.send({ to: '+13125550001', from: '+13125550002', text: 'Hello' });
} catch (err) {
  if (err instanceof Telnyx.APIConnectionError) {
    console.error('Network error — check connectivity and retry');
  } else if (err instanceof Telnyx.RateLimitError) {
    // 429: rate limited — wait, then retry the request (bounded exponential backoff)
    const retryAfter = err.headers?.['retry-after'] || 1;
    await new Promise(r => setTimeout(r, retryAfter * 1000));
    // ...retry the call here (give up after a few attempts)
  } else if (err instanceof Telnyx.APIError) {
    console.error(`API error ${err.status}: ${err.message}`);
    if (err.status === 422) {
      console.error('Validation error — check required fields and formats');
    }
  }
  throw err; // Re-throw: a failed request must never look like success to the caller
}

Common error codes: 401 invalid API key, 403 insufficient permissions, 404 resource not found, 422 validation error (check field formats), 429 rate limited (retry with exponential backoff).

Important Notes

• Phone numbers must be in E.164 format (e.g., +13125550001). Include the + prefix and country code. No spaces, dashes, or parentheses.
• Pagination: List methods return an auto-paginating iterator. Use for await (const item of result) { ... } to iterate through all pages automatically.

List all Fax Applications

This endpoint returns a list of your Fax Applications inside the 'data' attribute of the response. You can adjust which applications are listed by using filters. Fax Applications are used to configure how you send and receive faxes using the Programmable Fax API with Telnyx.

GET /fax_applications

// Automatically fetches more pages as needed.
for await (const faxApplication of client.faxApplications.list()) {
  console.log(faxApplication.id);
}

Returns: active (boolean), anchorsite_override (enum: Latency, Chicago, IL, Ashburn, VA, San Jose, CA, Sydney, Australia, Amsterdam, Netherlands, London, UK, Toronto, Canada, Vancouver, Canada, Frankfurt, Germany), application_name (string), created_at (string), id (string), inbound (object), outbound (object), record_type (string), tags (array[string]), updated_at (string), webhook_event_failover_url (uri), webhook_event_url (uri), webhook_timeout_secs (integer | null)

Creates a Fax Application

Creates a new Fax Application based on the parameters sent in the request. The application name and webhook URL are required. Once created, you can assign phone numbers to your application using the /phone_numbers endpoint.

POST /fax_applications — Required: application_name, webhook_event_url

Optional: active (boolean), anchorsite_override (enum: Latency, Chicago, IL, Ashburn, VA, San Jose, CA, Sydney, Australia, Amsterdam, Netherlands, London, UK, Toronto, Canada, Vancouver, Canada, Frankfurt, Germany), inbound (object), outbound (object), tags (array[string]), webhook_event_failover_url (uri), webhook_timeout_secs (integer | null)

const faxApplication = await client.faxApplications.create({
  application_name: 'fax-router',
  webhook_event_url: 'https://example.com',
});

console.log(faxApplication.data);

Returns: active (boolean), anchorsite_override (enum: Latency, Chicago, IL, Ashburn, VA, San Jose, CA, Sydney, Australia, Amsterdam, Netherlands, London, UK, Toronto, Canada, Vancouver, Canada, Frankfurt, Germany), application_name (string), created_at (string), id (string), inbound (object), outbound (object), record_type (string), tags (array[string]), updated_at (string), webhook_event_failover_url (uri), webhook_event_url (uri), webhook_timeout_secs (integer | null)

Retrieve a Fax Application

Return the details of an existing Fax Application inside the 'data' attribute of the response.

GET /fax_applications/{id}

const faxApplication = await client.faxApplications.retrieve('1293384261075731499');

console.log(faxApplication.data);

Returns: active (boolean), anchorsite_override (enum: Latency, Chicago, IL, Ashburn, VA, San Jose, CA, Sydney, Australia, Amsterdam, Netherlands, London, UK, Toronto, Canada, Vancouver, Canada, Frankfurt, Germany), application_name (string), created_at (string), id (string), inbound (object), outbound (object), record_type (string), tags (array[string]), updated_at (string), webhook_event_failover_url (uri), webhook_event_url (uri), webhook_timeout_secs (integer | null)

Update a Fax Application

Updates settings of an existing Fax Application based on the parameters of the request.

PATCH /fax_applications/{id} — Required: application_name, webhook_event_url

Optional: active (boolean), anchorsite_override (enum: Latency, Chicago, IL, Ashburn, VA, San Jose, CA, Sydney, Australia, Amsterdam, Netherlands, London, UK, Toronto, Canada, Vancouver, Canada, Frankfurt, Germany), fax_email_recipient (string | null), inbound (object), outbound (object), tags (array[string]), webhook_event_failover_url (uri), webhook_timeout_secs (integer | null)

const faxApplication = await client.faxApplications.update('1293384261075731499', {
  application_name: 'fax-router',
  webhook_event_url: 'https://example.com',
});

console.log(faxApplication.data);

Returns: active (boolean), anchorsite_override (enum: Latency, Chicago, IL, Ashburn, VA, San Jose, CA, Sydney, Australia, Amsterdam, Netherlands, London, UK, Toronto, Canada, Vancouver, Canada, Frankfurt, Germany), application_name (string), created_at (string), id (string), inbound (object), outbound (object), record_type (string), tags (array[string]), updated_at (string), webhook_event_failover_url (uri), webhook_event_url (uri), webhook_timeout_secs (integer | null)

Deletes a Fax Application

Permanently deletes a Fax Application. Deletion may be prevented if the application is in use by phone numbers.

DELETE /fax_applications/{id}

const faxApplication = await client.faxApplications.delete('1293384261075731499');

console.log(faxApplication.data);

Returns: active (boolean), anchorsite_override (enum: Latency, Chicago, IL, Ashburn, VA, San Jose, CA, Sydney, Australia, Amsterdam, Netherlands, London, UK, Toronto, Canada, Vancouver, Canada, Frankfurt, Germany), application_name (string), created_at (string), id (string), inbound (object), outbound (object), record_type (string), tags (array[string]), updated_at (string), webhook_event_failover_url (uri), webhook_event_url (uri), webhook_timeout_secs (integer | null)

View a list of faxes

Retrieve a paginated list of faxes sent or received on your account.

GET /faxes

// Automatically fetches more pages as needed.
for await (const fax of client.faxes.list()) {
  console.log(fax.id);
}

Returns: client_state (string), connection_id (string), created_at (date-time), direction (enum: inbound, outbound), failure_reason (string | null), from (string), from_display_name (string), id (uuid), internal_failure_reason (string | null), media_name (string), media_url (string), preview_url (string), quality (enum: normal, high, very_high, ultra_light, ultra_dark), record_type (enum: fax), status (enum: queued, media.processed, originated, sending, delivered, failed, initiated, receiving, media.processing, received), store_media (boolean), stored_media_url (string), to (string), updated_at (date-time), webhook_failover_url (string), webhook_url (string)

Send a fax

Send a fax. Files have size limits and page count limit validations. If a file is bigger than 50MB or has more than 350 pages it will fail with file_size_limit_exceeded and page_count_limit_exceeded respectively.

POST /faxes — Required: connection_id, from, to

Optional: black_threshold (integer), client_state (string), from_display_name (string), media_name (string), media_url (string), monochrome (boolean), preview_format (enum: pdf, tiff), quality (enum: normal, high, very_high, ultra_light, ultra_dark), store_media (boolean), store_preview (boolean), t38_enabled (boolean), webhook_url (string)

const fax = await client.faxes.create({
  connection_id: '234423',
  from: '+13125790015',
  to: '+13127367276',
    media_url: 'https://example.com/document.pdf',
});

console.log(fax.data);

Returns: client_state (string), connection_id (string), created_at (date-time), direction (enum: inbound, outbound), failure_reason (string | null), from (string), from_display_name (string), id (uuid), internal_failure_reason (string | null), media_name (string), media_url (string), preview_url (string), quality (enum: normal, high, very_high, ultra_light, ultra_dark), record_type (enum: fax), status (enum: queued, media.processed, originated, sending, delivered, failed, initiated, receiving, media.processing, received), store_media (boolean), stored_media_url (string), to (string), updated_at (date-time), webhook_failover_url (string), webhook_url (string)

View a fax

Returns the details of a single fax, including its current status.

GET /faxes/{id}

const fax = await client.faxes.retrieve('182bd5e5-6e1a-4fe4-a799-aa6d9a6ab26e');

console.log(fax.data);

Returns: client_state (string), connection_id (string), created_at (date-time), direction (enum: inbound, outbound), failure_reason (string | null), from (string), from_display_name (string), id (uuid), internal_failure_reason (string | null), media_name (string), media_url (string), preview_url (string), quality (enum: normal, high, very_high, ultra_light, ultra_dark), record_type (enum: fax), status (enum: queued, media.processed, originated, sending, delivered, failed, initiated, receiving, media.processing, received), store_media (boolean), stored_media_url (string), to (string), updated_at (date-time), webhook_failover_url (string), webhook_url (string)

Delete a fax

Delete a fax resource from your account.

DELETE /faxes/{id}

await client.faxes.delete('182bd5e5-6e1a-4fe4-a799-aa6d9a6ab26e');

Cancel a fax

Cancel the outbound fax that is in one of the following states: queued, media.processed, originated or sending

POST /faxes/{id}/actions/cancel

const response = await client.faxes.actions.cancel('182bd5e5-6e1a-4fe4-a799-aa6d9a6ab26e');

console.log(response.data);

Returns: result (string)

Refresh a fax

Refreshes the inbound fax's media_url when it has expired

POST /faxes/{id}/actions/refresh

const response = await client.faxes.actions.refresh('182bd5e5-6e1a-4fe4-a799-aa6d9a6ab26e');

console.log(response.data);

Returns: result (string)

Webhooks

Webhook Verification

Telnyx signs webhooks with Ed25519. Each request includes telnyx-signature-ed25519 and telnyx-timestamp headers. Always verify signatures in production:

Verification needs your account's public key (Mission Control Portal → API Keys → Public Key). The SDK reads it from TELNYX_PUBLIC_KEY (the ## Setup block above passes it explicitly); without it every valid webhook fails verification and the handler below returns 400.

// In your webhook handler (e.g., Express — use raw body, not parsed JSON):
app.post('/webhooks', express.raw({ type: 'application/json' }), async (req, res) => {
  try {
    const event = await client.webhooks.unwrap(req.body.toString(), {
      headers: req.headers,
    });
    // Signature valid — event is the parsed webhook payload
    console.log('Received event:', event.data.event_type);
    res.status(200).send('OK');
  } catch (err) {
    console.error('Webhook verification failed:', err.message);
    res.status(400).send('Invalid signature');
  }
});

The following webhook events are sent to your configured webhook URL. All webhooks include telnyx-timestamp and telnyx-signature-ed25519 headers for Ed25519 signature verification. Use client.webhooks.unwrap() to verify.

Webhook payload fields

`fax.delivered`

`fax.failed`

`fax.media.processed`

`fax.queued`

`fax.sending.started`