> ## Documentation Index
> Fetch the complete documentation index at: https://docs.thinnest.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# SMS Mid-Call

> Send text messages to the caller during an active voice call — confirmations, links, codes, and more.

# SMS Mid-Call

The **SMS Mid-Call** tool lets your voice agent send a text message to the caller while the call is still active. This is useful for sharing information that's hard to communicate over the phone — links, confirmation codes, addresses, or appointment details.

## When to Use

* Send a booking confirmation link during a scheduling call
* Share a payment URL while discussing billing
* Send a verification code for caller authentication
* Provide a tracking number or order details
* Share directions or an address

## How It Works

```
Caller: "Can you send me the link to reset my password?"
Agent: "Absolutely, I'm sending it to your phone now."
→ SMS sent: "Reset your password here: https://acme.com/reset?token=abc123"
Agent: "Done! You should receive it in a moment. Is there anything else?"
```

The SMS is sent to the caller's phone number (the number they called from or the number you dialed for outbound calls).

## Configuration

### Via the Dashboard

1. Open your agent and scroll to **Voice Settings**.
2. Enable **SMS Mid-Call**.
3. Choose your SMS provider:

| Provider       | Description                                                    |
| -------------- | -------------------------------------------------------------- |
| **Twilio**     | Uses your Twilio account or the platform's default credentials |
| **Custom API** | Send SMS via any HTTPS endpoint                                |

4. Configure message templates (optional).
5. Click **Save**.

### Via the API

```bash theme={null}
curl -X PATCH https://api.thinnest.ai/agents/agent_abc123 \
  -H "Authorization: Bearer $THINNESTAI_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "voice_tools": {
      "sms_mid_call": {
        "enabled": true,
        "provider": "twilio",
        "from_number": "+14155550000",
        "templates": {
          "booking_confirmation": "Your appointment is confirmed for {date} at {time}. Details: {link}",
          "password_reset": "Reset your password: {link}"
        }
      }
    }
  }'
```

## System Prompt Guidance

```
When a caller needs a link, confirmation code, or any detailed information,
send it via SMS during the call. Always confirm with the caller that you're
sending the text message, and verify they received it before ending the call.

Use the booking_confirmation template when confirming appointments.
Use the password_reset template when the caller needs to reset their password.
```

## Custom SMS Provider

If you use a provider other than Twilio, configure a custom API endpoint:

```bash theme={null}
curl -X PATCH https://api.thinnest.ai/agents/agent_abc123 \
  -H "Authorization: Bearer $THINNESTAI_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "voice_tools": {
      "sms_mid_call": {
        "enabled": true,
        "provider": "custom",
        "custom_api_url": "https://api.your-sms-provider.com/v1/sms/send",
        "custom_api_headers": {
          "Authorization": "Bearer YOUR_SMS_API_KEY"
        }
      }
    }
  }'
```

The custom endpoint receives a POST request with:

```json theme={null}
{
  "to": "+14155551234",
  "message": "Your appointment is confirmed for March 10 at 2:00 PM."
}
```