Telnyx Fax - curl

Installation

# curl is pre-installed on macOS, Linux, and Windows 10+

Setup

export TELNYX_API_KEY="YOUR_API_KEY_HERE"

All examples below use $TELNYX_API_KEY for authentication.

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:

# Check HTTP status code in response
response=$(curl -s -w "\n%{http_code}" \
  -X POST "https://api.telnyx.com/v2/messages" \
  -H "Authorization: Bearer $TELNYX_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"to": "+13125550001", "from": "+13125550002", "text": "Hello"}')

http_code=$(echo "$response" | tail -1)
body=$(echo "$response" | sed '$d')

case $http_code in
  2*) echo "Success: $body" ;;
  422) echo "Validation error — check required fields and formats" ;;
  429) echo "Rate limited — retry after delay"; sleep 1 ;;
  401) echo "Authentication failed — check TELNYX_API_KEY" ;;
  *)   echo "Error $http_code: $body" ;;
esac

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 endpoints return paginated results. Use page[number] and page[size] query parameters to navigate pages. Check meta.total_pages in the response.

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

curl -H "Authorization: Bearer $TELNYX_API_KEY" "https://api.telnyx.com/v2/fax_applications?sort=application_name"

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)

curl \
  -X POST \
  -H "Authorization: Bearer $TELNYX_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
  "application_name": "call-router",
  "active": false,
  "anchorsite_override": "Amsterdam, Netherlands",
  "webhook_event_url": "https://example.com",
  "webhook_event_failover_url": "https://failover.example.com",
  "webhook_timeout_secs": 25,
  "tags": [
    "tag1",
    "tag2"
  ]
}' \
  "https://api.telnyx.com/v2/fax_applications"

Retrieve a Fax Application

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

GET /fax_applications/{id}

curl -H "Authorization: Bearer $TELNYX_API_KEY" "https://api.telnyx.com/v2/fax_applications/1293384261075731499"

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)

curl \
  -X PATCH \
  -H "Authorization: Bearer $TELNYX_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
  "application_name": "call-router",
  "active": false,
  "anchorsite_override": "Amsterdam, Netherlands",
  "webhook_event_url": "https://example.com",
  "webhook_event_failover_url": "https://failover.example.com",
  "webhook_timeout_secs": 25,
  "fax_email_recipient": "user@example.com",
  "tags": [
    "tag1",
    "tag2"
  ]
}' \
  "https://api.telnyx.com/v2/fax_applications/1293384261075731499"

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}

curl \
  -X DELETE \
  -H "Authorization: Bearer $TELNYX_API_KEY" \
  "https://api.telnyx.com/v2/fax_applications/1293384261075731499"

View a list of faxes

GET /faxes

curl -H "Authorization: Bearer $TELNYX_API_KEY" "https://api.telnyx.com/v2/faxes"

Returns: client_state (string), connection_id (string), created_at (date-time), direction (enum: inbound, outbound), from (string), from_display_name (string), id (uuid), 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)

curl \
  -X POST \
  -H "Authorization: Bearer $TELNYX_API_KEY" \
  -F "connection_id=234423" \
  -F "contents=@/path/to/file" \
  -F "to=+13127367276" \
  -F "from=+13125790015" \
  -F "quality=high" \
  "https://api.telnyx.com/v2/faxes"

View a fax

GET /faxes/{id}

curl -H "Authorization: Bearer $TELNYX_API_KEY" "https://api.telnyx.com/v2/faxes/{id}"

Delete a fax

DELETE /faxes/{id}

curl \
  -X DELETE \
  -H "Authorization: Bearer $TELNYX_API_KEY" \
  "https://api.telnyx.com/v2/faxes/{id}"

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

curl \
  -X POST \
  -H "Authorization: Bearer $TELNYX_API_KEY" \
  -H "Content-Type: application/json" \
  "https://api.telnyx.com/v2/faxes/{id}/actions/cancel"

Returns: result (string)

Refresh a fax

Refreshes the inbound fax's media_url when it has expired

POST /faxes/{id}/actions/refresh

curl \
  -X POST \
  -H "Authorization: Bearer $TELNYX_API_KEY" \
  -H "Content-Type: application/json" \
  "https://api.telnyx.com/v2/faxes/{id}/actions/refresh"

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:

# Telnyx signs webhooks with Ed25519 (asymmetric — NOT HMAC/Standard Webhooks).
# Headers sent with each webhook:
#   telnyx-signature-ed25519: base64-encoded Ed25519 signature
#   telnyx-timestamp: Unix timestamp (reject if >5 minutes old for replay protection)
#
# Get your public key from: Telnyx Portal > Account Settings > Keys & Credentials
# Use the Telnyx SDK in your language for verification (client.webhooks.unwrap).
# Your endpoint MUST return 2xx within 2 seconds or Telnyx will retry (up to 3 attempts).
# Configure a failover URL in Telnyx Portal for additional reliability.

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.

Event	Description
`fax.delivered`	Fax Delivered
`fax.failed`	Fax Failed
`fax.media.processed`	Fax Media Processed
`fax.queued`	Fax Queued
`fax.sending.started`	Fax Sending Started

Webhook payload fields

fax.delivered

Field	Type	Description
`data.record_type`	enum: event	Identifies the type of the resource.
`data.id`	uuid	Identifies the type of resource.
`data.occurred_at`	date-time	ISO 8601 datetime of when the event occurred.
`data.event_type`	enum: fax.delivered	The type of event being delivered.
`data.payload.call_duration_secs`	integer	The duration of the call in seconds.
`data.payload.connection_id`	string	The ID of the connection used to send the fax.
`data.payload.direction`	enum: inbound, outbound	The direction of the fax.
`data.payload.fax_id`	uuid	Identifies the fax.
`data.payload.original_media_url`	string	The original URL to the PDF used for the fax's media.
`data.payload.media_name`	string	The media_name used for the fax's media.
`data.payload.to`	string	The phone number, in E.164 format, the fax will be sent to or SIP URI
`data.payload.from`	string	The phone number, in E.164 format, the fax will be sent from.
`data.payload.user_id`	uuid	Identifier of the user to whom the fax belongs
`data.payload.page_count`	integer	Number of transferred pages
`data.payload.status`	enum: delivered	The status of the fax.
`data.payload.client_state`	string	State received from a command.
`meta.attempt`	integer	The delivery attempt number.
`meta.delivered_to`	uri	The URL the webhook was delivered to.

fax.failed

Field	Type	Description
`data.record_type`	enum: event	Identifies the type of the resource.
`data.id`	uuid	Identifies the type of resource.
`data.occurred_at`	date-time	ISO 8601 datetime of when the event occurred.
`data.event_type`	enum: fax.failed	The type of event being delivered.
`data.payload.connection_id`	string	The ID of the connection used to send the fax.
`data.payload.direction`	enum: inbound, outbound	The direction of the fax.
`data.payload.fax_id`	uuid	Identifies the fax.
`data.payload.original_media_url`	string	The original URL to the PDF used for the fax's media.
`data.payload.media_name`	string	The media_name used for the fax's media.
`data.payload.to`	string	The phone number, in E.164 format, the fax will be sent to or SIP URI
`data.payload.from`	string	The phone number, in E.164 format, the fax will be sent from.
`data.payload.user_id`	uuid	Identifier of the user to whom the fax belongs
`data.payload.failure_reason`	enum: rejected	Cause of the sending failure
`data.payload.status`	enum: failed	The status of the fax.
`data.payload.client_state`	string	State received from a command.
`meta.attempt`	integer	The delivery attempt number.
`meta.delivered_to`	uri	The URL the webhook was delivered to.

fax.media.processed

Field	Type	Description
`data.record_type`	enum: event	Identifies the type of the resource.
`data.id`	uuid	Identifies the type of resource.
`data.occurred_at`	date-time	ISO 8601 datetime of when the event occurred.
`data.event_type`	enum: fax.media.processed	The type of event being delivered.
`data.payload.connection_id`	string	The ID of the connection used to send the fax.
`data.payload.direction`	enum: inbound, outbound	The direction of the fax.
`data.payload.fax_id`	uuid	Identifies the fax.
`data.payload.original_media_url`	string	The original URL to the PDF used for the fax's media.
`data.payload.media_name`	string	The media_name used for the fax's media.
`data.payload.to`	string	The phone number, in E.164 format, the fax will be sent to or SIP URI
`data.payload.from`	string	The phone number, in E.164 format, the fax will be sent from.
`data.payload.user_id`	uuid	Identifier of the user to whom the fax belongs
`data.payload.status`	enum: media.processed	The status of the fax.
`data.payload.client_state`	string	State received from a command.
`meta.attempt`	integer	The delivery attempt number.
`meta.delivered_to`	uri	The URL the webhook was delivered to.

fax.queued

Field	Type	Description
`data.record_type`	enum: event	Identifies the type of the resource.
`data.id`	uuid	Identifies the type of resource.
`data.occurred_at`	date-time	ISO 8601 datetime of when the event occurred.
`data.event_type`	enum: fax.queued	The type of event being delivered.
`data.payload.connection_id`	string	The ID of the connection used to send the fax.
`data.payload.direction`	enum: inbound, outbound	The direction of the fax.
`data.payload.fax_id`	uuid	Identifies the fax.
`data.payload.original_media_url`	string	The original URL to the PDF used for the fax's media.
`data.payload.media_name`	string	The media_name used for the fax's media.
`data.payload.to`	string	The phone number, in E.164 format, the fax will be sent to or SIP URI
`data.payload.from`	string	The phone number, in E.164 format, the fax will be sent from.
`data.payload.user_id`	uuid	Identifier of the user to whom the fax belongs
`data.payload.status`	enum: queued	The status of the fax.
`data.payload.client_state`	string	State received from a command.
`meta.attempt`	integer	The delivery attempt number.
`meta.delivered_to`	uri	The URL the webhook was delivered to.

fax.sending.started

Field	Type	Description
`data.record_type`	enum: event	Identifies the type of the resource.
`data.id`	uuid	Identifies the type of resource.
`data.occurred_at`	date-time	ISO 8601 datetime of when the event occurred.
`data.event_type`	enum: fax.sending.started	The type of event being delivered.
`data.payload.connection_id`	string	The ID of the connection used to send the fax.
`data.payload.direction`	enum: inbound, outbound	The direction of the fax.
`data.payload.fax_id`	uuid	Identifies the fax.
`data.payload.original_media_url`	string	The original URL to the PDF used for the fax's media.
`data.payload.media_name`	string	The media_name used for the fax's media.
`data.payload.to`	string	The phone number, in E.164 format, the fax will be sent to or SIP URI
`data.payload.from`	string	The phone number, in E.164 format, the fax will be sent from.
`data.payload.user_id`	uuid	Identifier of the user to whom the fax belongs
`data.payload.status`	enum: sending	The status of the fax.
`data.payload.client_state`	string	State received from a command.
`meta.attempt`	integer	The delivery attempt number.
`meta.delivered_to`	uri	The URL the webhook was delivered to.

telnyx-fax-curl