***

title: SIP Integration with Five9
subtitle: null
slug: sip-with-five9
description: null
-----------------

<Note>
  SIP trunking is only available on the Synthflow Enterprise Plan.
</Note>

This guide covers connecting a Five9 Virtual Contact Center (VCC) to Synthflow via SIP trunk for both inbound and outbound calling. Five9 can route calls to a Synthflow AI agent, and Synthflow can initiate outbound calls or transfer back to live Five9 agents.

## Prerequisites

| Requirement  | Detail                                                                               |
| ------------ | ------------------------------------------------------------------------------------ |
| Five9        | Active VCC account with Admin access and SIP Trunking enabled                        |
| Synthflow    | Enterprise Plan with a configured AI assistant (v2.0+)                               |
| Phone Number | At least one DID provisioned in Five9 (E.164 format)                                 |
| Network      | Firewall allows SIP (UDP/TCP 32681 or TLS 32682) and RTP between Five9 and Synthflow |

## Five9 Configuration

All configuration is done in the Five9 VCC Administrator console.

### Create the SIP Trunk

1. Go to **SIP Trunks** → **Add SIP Trunk**.
2. Select **Generic** in the Country dropdown, then choose **Generic VoIP Provider**.
3. Enter the SIP trunk main number in E.164 format (e.g. `+1XXXXXXXXXX`). Click **OK**.
4. Configure the trunk:

| Field                                       | Value                                               |
| ------------------------------------------- | --------------------------------------------------- |
| Name                                        | Synthflow AI                                        |
| Registrar / Server / Gateway Hostname or IP | `sip.synthflow.ai`                                  |
| Number of Simultaneous Calls                | Per your license / expected concurrent volume       |
| Type of Authentication                      | IP-based (whitelist Synthflow IPs) or Digest        |
| SIP Authentication ID                       | From Synthflow — only required if using Digest auth |
| Password                                    | From Synthflow — only required if using Digest auth |

5. Click **OK** to save.

<Note>
  IP-based authentication is the simpler option — contact Synthflow support for the current signaling IP list and add those IPs to your Five9 allowlist. No credentials are needed. Digest (credential-based) auth is also supported if your Five9 configuration requires it.
</Note>

### Configure Inbound Calling (Caller → Five9 → Synthflow)

Route incoming calls from your Five9 IVR or skill group to the Synthflow AI agent.

1. In your Five9 IVR script (or campaign skill), add a **Transfer** module.
2. Set the transfer destination to the DID associated with your Synthflow agent.
3. Select the **Synthflow AI** SIP trunk as the transfer path.
4. Alternatively, configure a skill-based routing rule that sends specific call types or overflow calls to the Synthflow trunk.

<Note>
  For after-hours routing, use Five9 schedule-based IVR branching to route to the Synthflow trunk when the contact center is closed.
</Note>

### Configure Outbound Calling (Five9 → Synthflow / Synthflow → PSTN)

Outbound rules control how Five9 routes calls through SIP trunks.

1. Go to **Outbound Rules** → **Add**.
2. Name the rule (e.g. `Route to Synthflow AI`).
3. Set matching criteria (dialed number prefix, skill group, user group, etc.).
4. Select the **Synthflow AI** trunk as the destination. Save.

For Synthflow-initiated outbound calls (AI agent calling a customer), Synthflow sends a SIP INVITE through the trunk. Five9 routes the call to the PSTN via the outbound rule.

## Synthflow Configuration

### Add the SIP Number

1. Go to the Synthflow **Phone Numbers** page.
2. Click **Add Number** → **Custom / SIP**.
3. Enter the phone number in E.164 format (same DID configured in Five9).
4. Fill in the SIP connection details:

| Field                        | Value                                                               |
| ---------------------------- | ------------------------------------------------------------------- |
| Termination URI              | Your Five9 SBC gateway IP or hostname (provided during trunk setup) |
| SIP Username                 | Your SIP authentication username                                    |
| SIP Password                 | Your SIP authentication password                                    |
| Outbound Proxy (if required) | Five9 SBC IP:port (only if Five9 requires a specific proxy)         |

<Note>
  The Termination URI is the Five9 gateway address — this is where Synthflow sends outbound calls. It is not `sip.synthflow.ai`.
</Note>

<Warning>
  Be precise when copying SIP credentials. Incorrect values will cause registration failure.
</Warning>

### Attach to the Assistant

1. Go to **Assistants** and create or select an assistant (v2.0+).
2. In the assistant settings, attach the SIP number you just created.
3. Wait 1–2 minutes for SIP registration to complete.

<Note>
  The SIP trunk is created at the moment of attaching the SIP number to the assistant.
</Note>

***

## Call Flow Summary

| Scenario                   | Flow                                                                   |
| -------------------------- | ---------------------------------------------------------------------- |
| Inbound to AI              | Caller → PSTN → Five9 VCC → IVR/Skill → SIP Trunk → Synthflow AI Agent |
| AI transfers to live agent | Synthflow AI → SIP transfer → Five9 VCC → Agent Queue → Live Agent     |
| Outbound from AI           | Synthflow AI → SIP INVITE → Five9 SIP Trunk → PSTN → Callee            |
| Outbound from Five9 via AI | Five9 campaign/IVR → SIP Trunk → Synthflow AI → handles call           |

***

## Verification

| Test                   | What to check                                                                                                               |
| ---------------------- | --------------------------------------------------------------------------------------------------------------------------- |
| Inbound call           | Call the Five9 DID from an external phone. Verify it routes through the IVR to the Synthflow AI agent. Check two-way audio. |
| Transfer to live agent | Trigger a transfer during a Synthflow call. Confirm the call lands in the correct Five9 queue with caller ID intact.        |
| Outbound from Five9    | Route a Five9 IVR/campaign call to the Synthflow trunk. Verify the AI agent answers.                                        |

***

## Quick Troubleshooting

| Issue                        | Fix                                                                                                   |
| ---------------------------- | ----------------------------------------------------------------------------------------------------- |
| Registration fails           | Check Termination URI, credentials, and firewall (UDP/TCP 32681 or TLS 32682).                        |
| Calls not reaching Synthflow | Verify Five9 outbound rule or IVR transfer points to the correct trunk. Confirm the trunk is enabled. |
| One-way or no audio          | Ensure RTP ports are open bidirectionally. Confirm G.711 codec on both sides.                         |
| Caller ID missing            | Set From header in E.164 format. Enable CNAM in Five9 VCC if needed.                                  |
| 302 errors                   | Five9 does not support 302 redirects. Use REFER or re-INVITE for transfers.                           |
| Call drops at 12 hours       | Five9 enforces a 12-hour call limit on SIP trunks. This is by design.                                 |

***

## Reference

* Five9 SIP Trunking Self-Service: documentation.five9.com/bundle/sip-trunking-self-service/
* Five9 Technical Requirements (IPs, ports): documentation.five9.com/bundle/technical-reqs/
* Synthflow SIP Overview: docs.synthflow\.ai/about-sip
* Synthflow X-EI SIP Header: docs.synthflow\.ai/x-ei-sip-header