---
title: "Create machine fax (HTTP 402 MPP challenge when unpaid)"
method: POST
path: "/api/v1/machine/faxes"
tags: ["machine"]
---

# Create machine fax (HTTP 402 MPP challenge when unpaid)

`POST /api/v1/machine/faxes`

## Request

- Base URL: `https://singlefax.com`
- URL: `https://singlefax.com/api/v1/machine/faxes`
- Auth: none required

No API key. Unpaid requests return 402 + WWW-Authenticate: Payment (Stripe SPT or Tempo USDC). x402 clients also see PAYMENT-REQUIRED when that rail is enabled. Retry with Authorization: Payment … or PAYMENT-SIGNATURE.

## Request body

- union
  - object
    - `to` string, required: Destination fax number in E.164
    - `base64` string, required: Original document encoded as base64 (PDF, Office, text, or image). Do not convert to PDF first. We convert before sending.
    - `uploadToken` string: Optional upload token instead of base64
    - `request_id` string, required: Client idempotency key for challenge + charge
    - `cover` boolean
  - object
    - `to` string, required: Destination fax number in E.164
    - `base64` string: Original document encoded as base64 (PDF, Office, text, or image). Do not convert to PDF first. We convert before sending.
    - `uploadToken` string, required: Optional upload token instead of base64
    - `request_id` string, required: Client idempotency key for challenge + charge
    - `cover` boolean

## Response `200`

Paid order

- object
  - `request_id` string, required
  - `id` string, required
  - `fulfillmentStatus` string
  - `paymentStatus` string
  - `replay` boolean

## Other responses

- `402`: Payment required (MPP challenge)
- `503`: Service unavailable

---

[API](https://skmtc.dev/singlefax/apis/singlefax-api.md) · [All operations](https://skmtc.dev/singlefax/apis/singlefax-api/llms.txt) · [OpenAPI document](https://skmtc.dev/singlefax/apis/singlefax-api/revisions/f6fdbfac1e25?raw)