Phone Number Transfers (TEL)

Phone number transfers (TEL) enable your AI agent to transfer calls directly to a standard phone number. This is the most common transfer type, ideal for routing calls to mobile phones, landlines, or call center queues.

Key Settings for Call Transfer

1. Phone Number to Call

• Specify the phone number that the assistant will transfer the call to. This can be a direct line or an extension within your organization. There is a validation button to confirm that the number is valid.

2. When Should the Transfer Take Place?

• This section defines the condition for the transfer. For example, you can set it to transfer when the user requests to speak to a manager or human agent.

3. Background Music

• Optionally enable background music during the transfer process to ensure a smooth and professional experience for the user while waiting for the transfer to be completed.

Transfer Modes

Human Detection (Warm Transfer)

When using a warm transfer (Message or Summary), the AI needs to deliver a briefing to the receiving agent. By default, the briefing plays as soon as the call connects — but that connection might be a voicemail greeting, an IVR menu, or empty air.

Human Detection solves this by waiting for a live human to answer before delivering the whisper message or summary. This ensures the briefing is heard by a real person, not wasted on an automated system.

Human Detection Timeout

Set how long the AI should wait for a human to be detected before giving up. If no human is detected within this window, the transfer is treated as failed and your configured failure handling applies.

Advanced Settings

In the Advanced Settings section, you can fine-tune the behavior of the call transfer action:

Hold Music

Enable background music to keep callers engaged while waiting for the transfer to complete. This provides a professional experience and reassures callers that they haven’t been disconnected.

To enable hold music:

1. Toggle Background Music in the transfer action settings
2. The default hold music will play while the recipient’s phone rings

Record the Call

By default, the recording stops once the call is transferred. If you want to continue recording the call, set the stop_recording_after_transfer parameter to false.

$
curl --location --request PUT 'https://api.synthflow.ai/v2/actions/<action_id>' \ 
>
--header 'Authorization: Bearer <api_key> \ 
>
--header 'Content-Type: application/json' \ 
>
--data '{ "LIVE_TRANSFER": { "stop_recording_after_transfer": false 
>
} 
>
}'

Transfer Failure Handling

What happens when a transfer fails depends on the transfer mode:

For warm transfers, you can configure fallback behavior:

• Have the agent apologize and offer to take a message
• Try an alternate transfer destination
• Schedule a callback for later

FAQs

How does Caller ID work?

Why the difference? Blind transfers use SIP REFER, which hands off the call entirely to your telephony provider, preserving the original caller ID. Warm transfers create a new outbound call leg (SIP DIAL) from Synthflow, so the agent’s number is shown.

What happens if a blind transfer fails?

The call between the AI agent and the customer ends immediately. There is no opportunity to retry or recover. If you need failure recovery, use a warm transfer instead.

Can I pass caller information to the receiving agent?

Yes, with warm transfers:

• Whisper message: Speak a custom message only the agent hears
• Context summary: AI generates a summary of the conversation
• Custom SIP headers: Pass structured data to your PBX (for SIP transfers)