Asterisk | Synthflow

When a caller asks a Synthflow agent for a human, the agent can warm-transfer the call to a human agent on an Asterisk-based PBX. Your PBX dialplan must accept the transfer request from Synthflow, and the agent needs a call transfer action in warm mode.

Warm transfer flow

Synthflow sends a new SIP INVITE to the human agent (the transferee).
When the human agent answers, Synthflow sends a REFER request on the original call with a Refer-To URI.
The Asterisk PBX accepts the REFER and opens a new channel to the Refer-To URI.
The Refer-To URI contains a random ID prefixed with 0875704225.
That URI bridges the caller and the human agent, which completes the warm transfer.

Asterisk dialplan

Add a from-synthflow context to your dialplan. In both examples, the first extension routes the call to the human agent’s number, +12345678912. The _0875704225. extension matches the Refer-To URI and dials back to Synthflow to bridge the call. Replace sip.synthflow.ai with your region’s SIP address if your workspace is in the US or EU region.

AEL (`extensions.ael`)

context from-synthflow {
  +12345678912 => {
    Dial(PJSIP/${EXTEN});
    Hangup();
  }
  _0875704225. => {
    Dial(PJSIP/synthflow/sip:${EXTEN}@sip.synthflow.ai:32681);
    Hangup();
  }
}

Classic dialplan (`extensions.conf`)

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

The _0875704225. extension pattern must match the prefix in the Refer-To URI, or the transfer does not complete.

Synthflow agent

Outbound agent

Select Agents in the left sidebar.
Create a new outbound agent.
Add a DID number. A test or dummy DID works.

Warm transfer action

Select Agents in the left sidebar, then select the agent.
Select Actions.
On the During the call tab, select Add Action → Call Transfer.
Enter the human agent’s phone number and select Add Actions. A new number prompts you to validate it.
Select the action you created, then select Transfer Settings.
Set Transfer Mode to Warm with message. You can enter a message the agent says before the transfer, for example “The user requested the manager, merging you now!” The transfer modes table lists what each mode does.
Select Save.

Transfer test

Select Agents in the left sidebar, then select the agent.
Under the agent’s name, select Test Agent.
Dial the number and start a conversation with the agent. Say “Please transfer to a human agent.”

Synthflow dials the transferee. When the human agent answers, they hear the configured message, and then the caller is merged into the call.