The fax API
developers actually like.

# send a fax. multipart. idempotent. signed webhooks.
curl "https://api.mintfax.com/v1/faxes" \
  -X POST \
  -H "Authorization: Bearer mfx_live_..." \
  -H "Idempotency-Key: $(uuidgen)" \
  -F "to=+15005550001" \
  -F "[email protected]" \
  -F "webhook_url=https://app.example.com/webhooks/fax" \
  -F "tags[patient_id]=p_19a8c"

import os, uuid, requests

resp = requests.post(
    "https://api.mintfax.com/v1/faxes",
    headers={
        "Authorization": f"Bearer {os.environ['MINTFAX_KEY']}",
        "Idempotency-Key": uuid.uuid4().hex,
    },
    data={
        "to": "+15005550001",
        "webhook_url": "https://app.example.com/webhooks/fax",
        "tags[patient_id]": "p_19a8c",
    },
    files={"file": open("statement.pdf", "rb")},
)

fax = resp.json()
print(fax["id"], fax["status"])  # fax_2K...  queued