Send fax
send_faxSend a PDF document to a fax number. WITHOUT API key: returns a Stripe checkout link (pay-per-fax from $2.49) – the fax is sent after the user pays. WITH a Mini/Flex subscription key (sff_...): sends immediately from the subscription quota. The document must be a direct, publicly accessible HTTPS link to a PDF (max. 10 MB). Supported: USA, Canada, Australia, New Zealand and 39 more countries (same list as sendfaxfast.com); premium-rate numbers are not supported. Each call transmits (or, for pay-per-fax, prepares the checkout for) a real fax to the given number. DOCUMENT (exactly one): "upload_id" from create_upload_link (for files on the user's device), "file" (a file attached in ChatGPT, filled in automatically), "document_url" (direct public HTTPS link to a PDF) or "document_base64" (tiny files only, max. 700 KB). For an attachment that is not available as "file", create_upload_link provides an upload link. The result states whether the fax was sent, scheduled or is awaiting payment.
Input Schema
| Name | Required | Description | Default |
|---|---|---|---|
| file | No | ChatGPT: the fax document the user attached in the chat (PDF, JPG or PNG). Filled in automatically by ChatGPT. | |
| No | Customer email for payment receipt and delivery confirmation (optional for pay-per-fax) | ||
| upload_id | No | upload_id returned by create_upload_link (after the user uploaded the file). One-time use. | |
| fax_number | Yes | Recipient fax number in E.164 format (e.g. +12125550100) | |
| document_url | No | Direct, publicly accessible HTTPS URL of the PDF document to fax (no login or preview pages) Alternative to upload_id / file. | |
| scheduled_at | No | ISO 8601 datetime to schedule the fax (e.g. 2026-10-08T09:00:00-05:00). Leave empty to send immediately. | |
| document_name | No | Optional: original file name of the document (e.g. "invoice.pdf"), shown on the transmission report. Not needed with upload_id or file. | |
| document_base64 | No | Only for very small files (max. 700 KB): the PDF, JPG or PNG as base64 or data: URI. Prefer create_upload_link. |