telnyx-fax-go

Telnyx Fax - Go

Installation

go get github.com/team-telnyx/telnyx-go

Setup

import (
  "context"
  "fmt"
  "os"

  "github.com/team-telnyx/telnyx-go"
  "github.com/team-telnyx/telnyx-go/option"
)

client := telnyx.NewClient(
  option.WithAPIKey(os.Getenv("TELNYX_API_KEY")),
)

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:

import "errors"

result, err := client.Messages.Send(ctx, params)
if err != nil {
  var apiErr *telnyx.Error
  if errors.As(err, &apiErr) {
    switch apiErr.StatusCode {
    case 422:
      fmt.Println("Validation error — check required fields and formats")
    case 429:
      // Rate limited — wait and retry with exponential backoff
      fmt.Println("Rate limited, retrying...")
    default:
      fmt.Printf("API error %d: %s\n", apiErr.StatusCode, apiErr.Error())
    }
  } else {
    fmt.Println("Network error — check connectivity and retry")
  }
}

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: Use ListAutoPaging() for automatic iteration: iter := client.Resource.ListAutoPaging(ctx, params); for iter.Next() { item := iter.Current() }.

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

	page, err := client.FaxApplications.List(context.Background(), telnyx.FaxApplicationListParams{})
	if err != nil {
		log.Fatal(err)
	}
	fmt.Printf("%+v\n", page)

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)

	faxApplication, err := client.FaxApplications.New(context.Background(), telnyx.FaxApplicationNewParams{
		ApplicationName: "fax-router",
		WebhookEventURL: "https://example.com",
	})
	if err != nil {
		log.Fatal(err)
	}
	fmt.Printf("%+v\n", 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}

	faxApplication, err := client.FaxApplications.Get(context.Background(), "1293384261075731499")
	if err != nil {
		log.Fatal(err)
	}
	fmt.Printf("%+v\n", 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)

	faxApplication, err := client.FaxApplications.Update(
		context.Background(),
		"1293384261075731499",
		telnyx.FaxApplicationUpdateParams{
			ApplicationName: "fax-router",
			WebhookEventURL: "https://example.com",
		},
	)
	if err != nil {
		log.Fatal(err)
	}
	fmt.Printf("%+v\n", 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}

	faxApplication, err := client.FaxApplications.Delete(context.Background(), "1293384261075731499")
	if err != nil {
		log.Fatal(err)
	}
	fmt.Printf("%+v\n", 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

GET /faxes

	page, err := client.Faxes.List(context.Background(), telnyx.FaxListParams{})
	if err != nil {
		log.Fatal(err)
	}
	fmt.Printf("%+v\n", page)

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)

	fax, err := client.Faxes.New(context.Background(), telnyx.FaxNewParams{
		ConnectionID: "234423",
		From:         "+13125790015",
		To:           "+13127367276",
		MediaURL: "https://example.com/document.pdf",
	})
	if err != nil {
		log.Fatal(err)
	}
	fmt.Printf("%+v\n", fax.Data)

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)

View a fax

GET /faxes/{id}

	fax, err := client.Faxes.Get(context.Background(), "182bd5e5-6e1a-4fe4-a799-aa6d9a6ab26e")
	if err != nil {
		log.Fatal(err)
	}
	fmt.Printf("%+v\n", fax.Data)

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)

Delete a fax

DELETE /faxes/{id}

	err := client.Faxes.Delete(context.Background(), "182bd5e5-6e1a-4fe4-a799-aa6d9a6ab26e")
	if err != nil {
		log.Fatal(err)
	}

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

	response, err := client.Faxes.Actions.Cancel(context.Background(), "182bd5e5-6e1a-4fe4-a799-aa6d9a6ab26e")
	if err != nil {
		log.Fatal(err)
	}
	fmt.Printf("%+v\n", response.Data)

Returns: result (string)

Refresh a fax

Refreshes the inbound fax's media_url when it has expired

POST /faxes/{id}/actions/refresh

	response, err := client.Faxes.Actions.Refresh(context.Background(), "182bd5e5-6e1a-4fe4-a799-aa6d9a6ab26e")
	if err != nil {
		log.Fatal(err)
	}
	fmt.Printf("%+v\n", 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:

// In your webhook handler:
func handleWebhook(w http.ResponseWriter, r *http.Request) {
  body, _ := io.ReadAll(r.Body)
  event, err := client.Webhooks.Unwrap(body, r.Header)
  if err != nil {
    http.Error(w, "Invalid signature", http.StatusBadRequest)
    return
  }
  // Signature valid — event is the parsed webhook payload
  fmt.Println("Received event:", event.Data.EventType)
  w.WriteHeader(http.StatusOK)
}

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.