> For a complete page index, fetch https://docs.synthflow.ai/llms.txt. For full documentation content, fetch https://docs.synthflow.ai/llms-full.txt. # Aircall > Connect Aircall to Synthflow via SIP trunking so AI agents can answer and transfer Aircall traffic. 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 | Requirement | Detail | | ------------ | --------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | Aircall | Active account with Admin access, and SIP or external routing turned on | | Synthflow | Enterprise plan with a configured agent | | Phone number | At least one DID provisioned in Aircall, in E.164 format | | Network | Firewall allows SIP (UDP/TCP `32681` or TLS `32682`) and RTP media between Aircall and Synthflow, from your region's [IP addresses](/ip-allow-lists#region-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: | Field | Value | | ------------------- | ----------------------------------------------------------------------------------- | | Name | `Synthflow AI` | | SIP URI | `sip.synthflow.ai`, or your region's [SIP address](/connect-over-sip#sip-addresses) | | Authentication Type | IP-based (allow list Synthflow's IPs) | | Port | `32681` (UDP/TCP) or `32682` (TLS) | | Transport | UDP/TCP or TLS | 4. Select **Save**. Aircall supports IP-based authentication. Add Synthflow's [SIP signaling addresses](/ip-allow-lists#region-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. > **Note** > > 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. > **Tip** > > 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](/sip-transfers) in Synthflow that routes to the Aircall SIP destination with that queue identifier. > **Warning** > > 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](/call-transfers#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](/phone-numbers#adding-custom-numbers) explains each field. | Field | Value | | ------------------ | ------------------------------------------------------------------- | | **SIP Domain** | Your Aircall SIP gateway hostname, from the Aircall SIP settings | | **Username** | Your Aircall SIP authentication username | | **Password** | Your Aircall SIP authentication password | | **Outbound Proxy** | Aircall'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. > **Warning** > > 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 | Scenario | Flow | | ------------------------ | ----------------------------------------------------------------------------------- | | Inbound to the agent | Caller → PSTN → Aircall → Smartflow → SIP forward → Synthflow agent | | Transfer to a live agent | Synthflow agent → new SIP INVITE → Aircall → team or user queue → live agent | | Overflow or after-hours | Aircall Smartflow (**Business Hours** condition) → Synthflow agent handles the call | ## Verification | Test | What to check | | ------------------------ | --------------------------------------------------------------------------------------------------------------------------------------------- | | Inbound call | Call 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 agent | Trigger a transfer during a Synthflow call. Check that the call lands in the correct Aircall team with the caller ID intact. | | Fallback routing | Let the Synthflow step time out. Check that the call falls back to the configured Aircall destination. | ## Troubleshooting | Issue | Fix | | ---------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------ | | Registration fails | Check the **SIP Domain** and SIP credentials. Check firewall rules for UDP/TCP `32681` or TLS `32682`. | | Calls do not reach Synthflow | Check that the Smartflow is published, the SIP forward step is active, and the Aircall SIP destination is turned on. | | One-way or no audio | Open RTP media ports in both directions. Check that both sides use G.711 (PCMU or PCMA). | | Transfer fails | Aircall 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 missing | Set the `From` header to the caller's E.164 number. Check that Aircall passes the ANI in the SIP INVITE. | ## Related resources * [Aircall Help Center](https://support.aircall.io), including the Smartflows documentation * [Telephony overview](/telephony-integrations) * [X-EI SIP header](/pass-call-context#x-ei-header) > Route Aircall calls to Synthflow agents over SIP and transfer them back to live agents.