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TELEPHONY

Aircall

Route Aircall calls to Synthflow agents over SIP and transfer them back to live agents.

Aircall forwards calls from its Smartflows to Synthflow over SIP, so a Synthflow agent answers calls that reach your Aircall contact center. The agent can handle inbound calls, qualify leads, and warm-transfer callers to live Aircall agents.

Prerequisites

RequirementDetail
AircallActive account with Admin access, and SIP or external routing turned on
SynthflowEnterprise plan with a configured agent
Phone numberAt least one DID provisioned in Aircall, in E.164 format
NetworkFirewall allows SIP (UDP/TCP 32681 or TLS 32682) and RTP media between Aircall and Synthflow, from your region’s IP addresses

Aircall configuration

You configure Aircall in the Aircall Dashboard (dashboard.aircall.io), under Integrations and Smartflows.

SIP destination

Aircall routes calls to external SIP destinations from its Smartflow builder. To add Synthflow as a destination:

  1. Go to Integrations → SIP / External SIP.
  2. Select Add SIP Destination.
  3. Configure the destination:
FieldValue
NameSynthflow AI
SIP URIsip.synthflow.ai, or your region’s SIP address
Authentication TypeIP-based (allow list Synthflow’s IPs)
Port32681 (UDP/TCP) or 32682 (TLS)
TransportUDP/TCP or TLS
  1. Select Save.

Aircall supports IP-based authentication. Add Synthflow’s SIP signaling addresses to the allow list. If your Aircall plan requires credential-based authentication, get the SIP username and password from Aircall, and enter them as Username and Password on the Synthflow number.

Aircall sends the SIP INVITE with the DID as the Request-URI. The Synthflow SIP number must match the DID provisioned in Aircall.

Smartflow routing

Route inbound calls to Synthflow with the Aircall Smartflow builder.

  1. Go to Numbers and select your inbound number.
  2. Select Edit Smartflow.
  3. Add a Forward to External SIP step.
  4. Select the Synthflow AI SIP destination you created.
  5. Set a timeout and a fallback destination, such as an Aircall team, for calls Synthflow does not answer. We recommend a 30-second timeout.
  6. Save and publish the Smartflow.

For after-hours or overflow routing, add a Business Hours condition before the Synthflow SIP step. Calls then go to the agent only when your live agents are unavailable.

Transfers back to Aircall

To let a Synthflow agent transfer a call back to a live Aircall agent:

  1. In the Aircall Dashboard, note the Line ID, Team ID, or User ID of the destination queue. These IDs appear in the dashboard URL when you view the line, team, or user.
  2. Configure a SIP transfer in Synthflow that routes to the Aircall SIP destination with that queue identifier.

Aircall does not support SIP REFER for mid-call transfers. Synthflow places a new outbound SIP INVITE to the agent queue instead, which is how warm transfer modes work. Contact Synthflow support for the recommended transfer configuration.

Synthflow configuration

SIP number

  1. In Synthflow, select Phone Numbers → New Phone Number → Import a Custom Number.
  2. Enter the phone number in E.164 format. Use the same DID that is provisioned in Aircall.
  3. Fill in the SIP connection details. Add a custom number explains each field.
FieldValue
SIP DomainYour Aircall SIP gateway hostname, from the Aircall SIP settings
UsernameYour Aircall SIP authentication username
PasswordYour Aircall SIP authentication password
Outbound ProxyAircall’s SIP proxy address and port, only if Aircall specifies one

The SIP Domain points back to Aircall. Synthflow sends outbound calls and transfers there.

Copy the SIP credentials exactly. Wrong values make registration fail.

Agent assignment

  1. Go to Agents and create or select an agent.
  2. Attach the SIP number you created to the agent. We create the SIP trunk at this moment.
  3. Wait one to two minutes for SIP registration to complete.

Call flows

ScenarioFlow
Inbound to the agentCaller → PSTN → Aircall → Smartflow → SIP forward → Synthflow agent
Transfer to a live agentSynthflow agent → new SIP INVITE → Aircall → team or user queue → live agent
Overflow or after-hoursAircall Smartflow (Business Hours condition) → Synthflow agent handles the call

Verification

TestWhat to check
Inbound callCall the Aircall DID from an external phone. Check that the Smartflow routes the call to the Synthflow agent, and that audio works both ways.
Transfer to a live agentTrigger a transfer during a Synthflow call. Check that the call lands in the correct Aircall team with the caller ID intact.
Fallback routingLet the Synthflow step time out. Check that the call falls back to the configured Aircall destination.

Troubleshooting

IssueFix
Registration failsCheck the SIP Domain and SIP credentials. Check firewall rules for UDP/TCP 32681 or TLS 32682.
Calls do not reach SynthflowCheck that the Smartflow is published, the SIP forward step is active, and the Aircall SIP destination is turned on.
One-way or no audioOpen RTP media ports in both directions. Check that both sides use G.711 (PCMU or PCMA).
Transfer failsAircall does not support SIP REFER, so Synthflow places a new outbound SIP INVITE to the agent queue. Contact Synthflow support for the configuration.
Caller ID missingSet the From header to the caller’s E.164 number. Check that Aircall passes the ANI in the SIP INVITE.