API documentation

Base URL: https://api.ineedtosendafax.com

Price: $1.49 per fax · US & Canada · up to 25 pages · min credit purchase $5.00. OpenAPI spec

Authentication

Send your key in the Authorization: Bearer header (or X-API-Key). Keys start with ifx_live_.

Send a fax

POST /v1/faxes        (multipart/form-data)
  to            required   recipient fax number (US/Canada)
  file          required   PDF, Word (DOC/DOCX), PostScript, or TIFF (max 32 MB, 25 pages)
  callback_url  optional   URL we POST to on completion
  cover         optional   "1" to add a cover page (default: none)
  cover_text    optional   message on the cover page
  recipient_name, sender_name  optional

curl -X POST https://api.ineedtosendafax.com/v1/faxes \
  -H "Authorization: Bearer ifx_live_..." \
  -F to=15551234567 -F file=@invoice.pdf
# 202
{"id":"","status":"queued","to":"15551234567","price_cents":149,"pages":1}

Idempotency

Send an Idempotency-Key header to safely retry. Repeats return the original job instead of sending again.

Status

GET /v1/faxes/{id}
GET /v1/faxes?limit=50
GET /v1/me          # balance, limits, usage
GET /v1/pricing

Statuses: queued → sending → sent | failed. Failed faxes are retried up to 5 times; if still undelivered, the credit is returned automatically.

Callbacks

If you set callback_url, we POST the final status there. Verify the X-Fax-Signature header with your webhook signing secret:

signature:  t=TIMESTAMP,v1=HEX
expected:   HMAC_SHA256(secret, TIMESTAMP + "." + raw_body)

Errors

{"error":{"code":"insufficient_credits","message":"..."}}

401 invalid/missing key · 402 insufficient credits · 400 validation · 413 too large · 429 rate limited.