SendFaxFast API

Send faxes directly from your software — no browser, no manual steps. The REST API is included in both subscription plans and is ready to use immediately after purchase.

Overview

The SendFaxFast API allows you to send faxes programmatically. It is suitable for:

Practice management software (Dampsoft, CGM, Medistar), ERP systems (SAP, Sage, Lexoffice), automation platforms (Zapier, Make), custom scripts and applications, and any other service that can send HTTP requests.

Authentication

Every API request requires your personal token in the Authorization header:

Authorization: Bearer sfx_xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

You can find your token at sendfaxfast.com/abo-portal.php. It always starts with sfx_. Do not share it — it grants full access to your subscription.

Limits & Plans

The limit is shared across faxes sent via the website and via the API. The remaining field in every response shows how many faxes you have left.

POST /send-fax.php

Sends a fax to the specified number. The PDF can be passed either as a URL or as a file upload.

Parameters

Option A — JSON Body (recommended)

Header: Content-Type: application/json

Option B — Multipart Upload

Header: Content-Type: multipart/form-data

Responses & Errors

{
  "success":   true,
  "fax_id":    "telnyx-uuid-123",
  "to":        "+14155551234",
  "from":      "+12125550199",
  "remaining": 6,
  "limit":     20
}

{
  "success": false,
  "error":   "Invalid or missing
Bearer Token."
}

{
  "success": false,
  "error":   "Monthly fax limit
reached (20 faxes)."
}

{
  "success": false,
  "error":   "Invalid fax number:
'+1 abc'. Use E.164 format."
}

Examples

cURL

curl -X POST https://sendfaxfast.com/send-fax.php \
  -H "Authorization: Bearer sfx_your_token" \
  -H "Content-Type: application/json" \
  -d '{
    "to":      "+14155551234",
    "pdf_url": "https://your-system.com/document.pdf"
  }'

Python

import requests

response = requests.post(
    "https://sendfaxfast.com/send-fax.php",
    headers={"Authorization": "Bearer sfx_your_token"},
    json={
        "to":      "+14155551234",
        "pdf_url": "https://your-system.com/document.pdf",
    }
)
data = response.json()
print(data["fax_id"], "sent,", data["remaining"], "faxes remaining")

PHP

$ch = curl_init('https://sendfaxfast.com/send-fax.php');
curl_setopt_array($ch, [
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_POST           => true,
    CURLOPT_POSTFIELDS     => json_encode([
        'to'      => '+14155551234',
        'pdf_url' => 'https://your-system.com/document.pdf',
    ]),
    CURLOPT_HTTPHEADER => [
        'Authorization: Bearer sfx_your_token',
        'Content-Type: application/json',
    ],
]);
$result = json_decode(curl_exec($ch), true);

Zapier / Make

URL:     https://sendfaxfast.com/send-fax.php
Method:  POST
Header:  Authorization: Bearer sfx_your_token
         Content-Type: application/json
Body:    { "to": "{{fax_number}}", "pdf_url": "{{pdf_link}}" }

FAQ

Do API faxes count toward my monthly limit?

Yes. Web faxes and API faxes share the same monthly limit. The remaining field in the response always shows the current count.

What happens when the limit is reached?

The API responds with HTTP 429 and an error message. The fax is not sent. The limit resets automatically on the first of next month.

Which PDF format is supported?

Standard PDF, max. 10 MB, max. 20 pages per fax. The URL must be publicly accessible without requiring a login.

Can I use my own fax number as the sender?

Yes. If you have your own fax number through your subscription, it will be used automatically as the sender. Replies to your fax will then arrive as a PDF in your email inbox.

How do I get my token?

After completing your subscription, you can find your token at sendfaxfast.com/abo-portal.php. Simply enter your email address — then view and copy your token.