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

Open your agent and scroll to Voice Settings.
Enable SMS Mid-Call.
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

Configure message templates (optional).
Click Save.

Via the API

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:

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:

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

SMS Mid-Call

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