Integrations

Transfer calls between Synthflow and Asterisk-based PBX systems

This guide outlines how warm transfers are handled between Synthflow and Asterisk-based PBX systems, and how to configure both your PBX and Synthflow UI for seamless call handoff to human agents.

How warm transfer works

When a caller asks the AI assistant (Synthflow) to speak to a human agent:

  1. Synthflow sends a new SIP INVITE to the human agent (transferee).
  2. Once the human agent answers, Synthflow sends a REFER request on the original call with a Refer-To: URI.
  3. The Asterisk PBX must accept the “ and open a new channel using the Refer-To URI.
  4. The Refer-To URI includes a random ID prefixed with 0875704225.
  5. This URI bridges the customer and the human agent, completing the warm transfer.

Asterisk PBX configuration

1. extensions.ael example

1context from-synthflow {
2  +12345678912 => {
3    Dial(PJSIP/${EXTEN});
4    Hangup();
5  }
6  _0875704225. => {
7    Dial(PJSIP/synthflow/sip:${EXTEN}@sip:sipin.synthflow.ai:32681);
8    Hangup();
9  }
10}

2. extensions.conf example

1[from-synthflow]
2exten => +12345678912,1,Dial(PJSIP/${EXTEN})
3same => n,Hangup()
4
5exten => _0875704225.,1,Dial(PJSIP/synthflow/sip:${EXTEN}@sip:sipin.synthflow.ai:32681)
6same => n,Hangup()

Note: The _0875704225. extension pattern must match the prefix used in the Refer-To URI to successfully complete the transfer.

Set up the warm transfer in Synthflow

Step 1. Create an outbound agent

1

Go to the Agents tab on the left-hand sidebar.

2

Create a new outbound agent. For more details on how to create an agent, see Create an agent.

3

Add a DID number (this can be a test/dummy DID if needed).

Step 2. Configure call actions for warm transfer

1

On the left-hand sidebar, click Agents.

2

Select the agent you want to configure the action for.

3

On the navigation sidebar, select Actions.

4

Switch to the During the call tab and click Add Action > Call Transfer.

5

Enter the phone number of the human agent and click Add Actions. If you’re adding a new number, you’ll be prompted to validate it.

6

Click on the action you’ve just created and select Transfer Settings.

7

Set Transfer Mode to “Warm transfer with message”. You can set a custom message the agent will say before transferring the call (for example, ““The user requested the manager; merging you now!”).

8

Click Save.

Test the warm transfer

1

On the left-hand sidebar, click Agents.

2

Select the agent you want to test.

3

On the nevigation sidebar under your agent’s nae, click Test Agent.

4

Dial the number and begin a conversation with the AI bot. In your conversation, say: “Please transfer to a human agent.” The system will dial the transferee. Once the agent answers, they will hear the configured prompt before being merged into the call.