---
name: sms-two-factor-auth
title: "SMS Two Factor Auth"
description: "Implement SMS-based two-factor authentication."
language: python
framework: flask
telnyx_products: [Cloud Storage, SMS/MMS, Verify]
---

# Production-ready OTP 2FA system with Flask and Telnyx SMS.

SMS application. Built with Telnyx Cloud Storage, Migration, Number Porting, SMS/MMS.

## Telnyx API Endpoints Used

- **Send Message (OTP)**: `POST /v2/messages` — [API reference](https://developers.telnyx.com/api/messaging/send-message)

## Architecture

```
  API Request
        │
        ▼
  ┌──────────────────┐
  │ Telnyx Messaging  │
  │ • Summarization    │
  └────────┬─────────┘
           │
           └──► JSON response
```

## Environment Variables

Copy `.env.example` to `.env` and fill in:

| Variable | Type | Example | Required | Description | Where to get it |
|----------|------|---------|----------|-------------|-----------------|
| `TELNYX_API_KEY` | `string` | `KEY0123456789ABCDEF` | **yes** | Telnyx API v2 key | [Portal](https://portal.telnyx.com/api-keys) |
| `OTP_EXPIRY_SECONDS` | `string` | `300` | no | Otp expiry seconds | — |
| `TELNYX_PHONE_NUMBER` | `string` | `your_value` | **yes** | Telnyx phone number | — |
| `FLASK_DEBUG` | `string` | `false` | no | Flask debug | — |

## Setup

```bash
git clone https://github.com/team-telnyx/telnyx-code-examples.git
cd telnyx-code-examples/sms-two-factor-auth-python
cp .env.example .env    # ← fill in your credentials
pip install -r requirements.txt
python app.py           # starts on http://localhost:5000
```

## API Reference

### `POST /auth/request-otp`

Request an OTP to be sent to the provided phone number.

```bash
curl -X POST http://localhost:5000/auth/request-otp \
  -H "Content-Type: application/json" \
  -d '{}'
```

**Response:**

```json
{
  "id": "item-1750280400",
  "status": "created",
  "created_at": "2026-07-15T14:30:00Z"
}
```

### `POST /auth/verify-otp`

Verify the OTP code provided by the user.

```bash
curl -X POST http://localhost:5000/auth/verify-otp \
  -H "Content-Type: application/json" \
  -d '{
    "phone": "+12125551234",
    "channel": "sms"
  }'
```

**Response:**

```json
{
  "verification_id": "ver-abc123",
  "status": "pending",
  "channel": "sms",
  "phone": "+12125551234"
}
```

### `GET /auth/otp-status`

Get OTP status for a phone number (for testing/debugging only).

```bash
curl http://localhost:5000/auth/otp-status
```

**Response:**

```json
{
  "items": [
    {
      "id": "item-001",
      "status": "active",
      "created_at": "2026-07-15T14:30:00Z"
    }
  ]
}
```

## Troubleshooting

| Issue | Cause | Fix |
|-------|-------|-----|
| `401 Unauthorized` | Invalid or missing API key | Verify `TELNYX_API_KEY` in `.env` matches your key in the [Portal](https://portal.telnyx.com/api-keys) |
| Webhook not received | Local server not publicly reachable | Expose it with a tunnel (e.g. ngrok) and set the webhook URL in the [Telnyx Portal](https://portal.telnyx.com) |
| `422 Unprocessable Entity` | Missing or malformed request fields | Check the request body against the API Reference above |

## Related Examples

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- [After Hours Nurse Triage (Python)](https://raw.githubusercontent.com/team-telnyx/telnyx-code-examples/main/after-hours-nurse-triage-python/README.md)
- [AI Appointment Booking SMS Flow (Python)](https://raw.githubusercontent.com/team-telnyx/telnyx-code-examples/main/ai-appointment-booking-sms-flow-python/README.md)
- [AI Appointment Reminder SMS Voice (Python)](https://raw.githubusercontent.com/team-telnyx/telnyx-code-examples/main/ai-appointment-reminder-sms-voice-python/README.md)

## Resources

- [Telnyx Developer Docs](https://developers.telnyx.com)
- [Telnyx Portal](https://portal.telnyx.com)

## Why Telnyx

Telnyx is an **AI Communications Infrastructure** platform — voice, messaging, SIP, AI, and IoT on one private, global network.