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Base URL

All API requests use the following base URL: 
https://api.mintfax.com/v1

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Authentication

Include your API key as a Bearer token in the Authorization header: 
Authorization: Bearer mfx_test_abc123...
Sandbox keys start with mfx_test_, live keys with mfx_live_. The registration endpoints (POST /account/register and POST /account/register/verify) do not require authentication.

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Request Format

  • JSON for request bodies (Content-Type: application/json)
  • Multipart for file uploads (Content-Type: multipart/form-data)

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Response Format

All responses return JSON. Successful responses return the resource directly. Error responses follow a consistent structure: 
{
  "error": "insufficient_balance",
  "message": "Insufficient balance to submit fax",
  "action": "top_up_balance",
  "docs": "/docs/errors#insufficient-balance"
}

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Idempotency

POST /fax accepts an optional idempotency_key form field. Duplicate requests with the same key return the original response without re-executing. Keys expire after 24 hours. See the Idempotency guide for details.

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Rate Limits

Rate limits are applied per API key. Current limits are returned in response headers:
  • X-RateLimit-Limit - requests per minute
  • X-RateLimit-Remaining - requests remaining in current window
  • X-RateLimit-Reset - seconds until the window resets

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Pagination

List endpoints return paginated results with 20 items per page. Use the page query parameter to navigate: 
GET /v1/faxes?page=2

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OpenAPI Spec

The machine-readable OpenAPI 3.1 spec is available at:
Last modified on May 11, 2026