SIP Trunk Setup for Vapi

Use Voyced as an external SIP provider

This guide explains how to connect your Voyced telephone number and SIP trunk to Vapi, allowing your AI voice assistant to make and receive telephone calls.

The setup uses Voyced's standard SIP connection details, including username, password and SIP server.

Vapi supports SIP registration and outbound authentication. Inbound calling also requires the correct incoming SIP source addresses to be configured and verified.

What You’ll Need

Before you begin, make sure you have:

• Access to your Vapi dashboard

• An active Vapi account with SIP trunk access

• A configured Vapi AI voice assistant

• A Vapi private API key

• An active Voyced telephone number

• Your Voyced SIP details:

  • Account / telephone number: Your-Voyced-DID

  • Service password: YourServicePassword

  • SIP server: sip.voyced.eu

Requirements Before You Begin

• Your Voyced account must be active.

• Your Voyced account must have sufficient calling credit and simultaneous call capacity.

• Vapi must have permission to establish outbound SIP connections.

• SIP registration must use the Voyced account credentials.

• SIP signalling uses UDP port 5060.

• Use full international telephone number format.

• Recommended audio codecs:

  • PCMA / G.711 A-law

  • PCMU / G.711 μ-law

• Confirm that Vapi and Voyced permit traffic between their SIP servers.

Vapi has separate US and EU environments. Use the environment associated with your Vapi account.

EU availability depends on your Vapi subscription and account region.

SIP Trunk Setup Steps

1. Log in to Vapi

1. Open your Vapi dashboard.

2. Log in using your account credentials.

3. Open Integrations.

4. Find Phone Number Providers.

5. Select SIP Trunk.

Vapi provides SIP trunk configuration through its dashboard and API.

For this manual, the API method provides the complete registration settings needed for Voyced.

2. Prepare Your Voyced Connection Details

Use the following settings:

The registration realm normally matches the server domain, but the actual value must match the realm supplied by Voyced in its SIP authentication challenge.

3. Create the Voyced SIP Trunk

Vapi supports a custom SIP trunk using its byo-sip-trunk credential type.

Open a terminal or API client.

For the US environment, set:

export VAPI_API_BASE_URL="https://api.vapi.ai"

For the EU environment, use:

export VAPI_API_BASE_URL="https://api.eu.vapi.ai"

Set your Vapi private API key:

export VAPI_PRIVATE_KEY="YOUR_VAPI_PRIVATE_KEY"

Create the Voyced SIP trunk:

curl -X POST "$VAPI_API_BASE_URL/credential" \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer $VAPI_PRIVATE_KEY" \
  -d '{
    "provider": "byo-sip-trunk",
    "name": "Voyced SIP Trunk",
    "gateways": [
      {
        "ip": "sip.voyced.eu",
        "port": 5060,
        "inboundEnabled": false,
        "outboundEnabled": true,
        "outboundProtocol": "udp"
      }
    ],
    "outboundLeadingPlusEnabled": false,
    "outboundAuthenticationPlan": {
      "authUsername": "Your-Voyced-DID",
      "authPassword": "YourServicePassword",
      "sipRegisterPlan": {
        "domain": "sip.voyced.eu",
        "username": "Your-Voyced-DID",
        "realm": "sip.voyced.eu"
      }
    }
  }'

This configuration:

• Connects Vapi to sip.voyced.eu.

• Uses your Voyced username and service password.

• Configures SIP registration with Voyced.

• Enables outbound calling.

• Leaves inbound gateway matching disabled until the correct Voyced signalling addresses are confirmed.

After creating the trunk, Vapi returns a credential ID.

Save this value:

YOUR_CREDENTIAL_ID

You will need it when adding your Voyced telephone number.

4. Add Your Voyced Telephone Number

Next, link your Voyced number to the SIP trunk.

In the Vapi dashboard:

1. Open Phone Numbers.

2. Select Create Phone Number.

3. Choose BYO SIP Trunk Number.

4. Select your Voyced SIP trunk credential.

5. Enter your Voyced telephone number.

Example:

You may also create the telephone number through Vapi's API:

curl -X POST "$VAPI_API_BASE_URL/phone-number" \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer $VAPI_PRIVATE_KEY" \
  -d '{
    "provider": "byo-phone-number",
    "name": "Voyced Number",
    "number": "Your-Voyced-DID",
    "numberE164CheckEnabled": false,
    "credentialId": "YOUR_CREDENTIAL_ID"
  }'

Replace Your-Voyced-DID with your actual telephone number, using digits only.

The example disables Vapi's E.164 validation to accommodate the placeholder and number formatting. With a correctly formatted E.164 number, normal validation is preferable.

Save the returned Phone Number ID:

YOUR_PHONE_NUMBER_ID

5. Configure Your AI Voice Assistant

1. Open the Vapi dashboard.

2. Navigate to Assistants.

3. Create a new assistant or select an existing one.

4. Configure:

   • Assistant name

   • Language

   • Voice

   • Opening message

   • Conversation instructions

5. Save your assistant.

Example:

Next:

1. Open Phone Numbers.

2. Select your Voyced number.

3. Locate Inbound Settings.

4. Select the assistant.

5. Save.

Your assistant is now associated with the Voyced telephone number inside Vapi.

6. Configure Outbound Calling

Vapi supports outbound calls through a configured BYO SIP trunk.

Once your Voyced trunk credentials are accepted, select your Voyced number as the calling number.

For a manual test:

1. Open Phone Numbers.

2. Select your Voyced number.

3. Open the outbound test panel.

4. Select your assistant.

5. Enter the destination number.

6. Start the call.

You may also place calls through the Vapi API.

Example:

curl -X POST "$VAPI_API_BASE_URL/call/phone" \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer $VAPI_PRIVATE_KEY" \
  -d '{
    "assistantId": "YOUR_ASSISTANT_ID",
    "customer": {
      "number": "442012345678",
      "numberE164CheckEnabled": false
    },
    "phoneNumberId": "YOUR_PHONE_NUMBER_ID"
  }'

Replace the destination number with a telephone number you are authorised to call.

The outbound call should follow this route:

Vapi AI Assistant
       ↓
Voyced SIP Trunk
       ↓
Destination Telephone

If the call fails, inspect the SIP authentication response and the destination number format.

7. Configure Inbound Calling

Vapi's inbound SIP security requires the actual IP addresses or networks from which the carrier sends incoming calls.

The SIP hostname sip.voyced.eu is suitable for outbound gateway configuration.

For inbound gateway matching, Vapi requires numeric IPv4 addresses.

Before enabling inbound calling:

1. Confirm that Vapi has successfully registered with Voyced.

2. Confirm that Voyced delivers incoming calls to the registered SIP contact.

3. Obtain the Voyced signalling IP addresses used for incoming calls.

4. Configure those addresses in the Vapi trunk's inbound gateway settings.

Do not assume the addresses returned by looking up sip.voyced.eu are the addresses used for incoming call signalling.

For an existing trunk, Vapi supports updating its gateway configuration through the credential API.

Example structure:

{
  "gateways": [
    {
      "ip": "sip.voyced.eu",
      "port": 5060,
      "inboundEnabled": false,
      "outboundEnabled": true,
      "outboundProtocol": "udp"
    },
    {
      "ip": "VOYCED_INBOUND_SIGNALLING_IP",
      "port": 5060,
      "netmask": 32,
      "inboundEnabled": true,
      "outboundEnabled": false
    }
  ]
}

Replace VOYCED_INBOUND_SIGNALLING_IP with the verified numerical address provided by Voyced.

Add all required signalling addresses, including failover addresses. Preserve the existing outbound gateway when updating.

Vapi must also match incoming calls to the correct phone number and assistant.

If the registered contact does not result in incoming calls reaching Vapi, ask Vapi to confirm support for inbound delivery through sipRegisterPlan for your account.

Do not substitute SIP URI forwarding for the normal Voyced registration method.

8. Configure Firewall and Network Access

Vapi publishes static SIP signalling addresses for its supported regions.

Use the addresses belonging to your Vapi account region.

Network requirements:

US media IP addresses are dynamic. The EU region uses its documented static media address.

Where Voyced requires IP allowlisting, the relevant Vapi source addresses must be approved.

Confirm that both sides permit the media traffic required for two-way audio.

Testing Your Setup

Outbound Test

1. Open your Vapi dashboard.

2. Select your Voyced telephone number.

3. Select your AI assistant.

4. Enter a valid external telephone number.

5. Start the call.

Verify:

• Vapi connects through Voyced.

• SIP authentication succeeds.

• The destination telephone rings.

• The correct caller ID appears.

• Audio works both ways.

• The AI assistant responds normally.

Inbound Test

After inbound registration and gateway matching have been confirmed:

1. Call your Voyced telephone number from a mobile.

2. Confirm the incoming SIP call reaches Vapi.

3. Check the correct assistant answers.

4. Speak to the assistant.

5. Confirm two-way audio.

If registration succeeds but inbound calls do not arrive, inspect the received SIP signalling and the carrier source address.

Troubleshooting

SIP Registration Fails

Check:

• SIP server: sip.voyced.eu

• Username: Your-Voyced-DID

• Password: YourServicePassword

• Registration domain

• Authentication realm

• UDP port 5060

A working outbound authentication configuration does not automatically prove SIP registration succeeded.

401 or 407 Error

These responses indicate authentication is required.

An initial 401 or 407 response is normal when the server challenges the client.

If the call or registration subsequently fails, check:

• Username

• Password

• SIP authentication realm

• Whether Vapi sends a second authenticated SIP request

403 Error

Check:

• Account status

• Authentication details

• Caller ID authorisation

• Outbound permissions

• Simultaneous call limits

• Any source IP restrictions

404 Error

Check:

• Dialled telephone number

• Number format

• SIP Request-URI

• Inbound DID mapping

• Correct assistant assignment

A 404 response does not always mean the same problem. Check which system returned the response.

Inbound Calls Do Not Arrive

Check:

• SIP registration status

• Registered contact address

• Actual inbound signalling IP addresses

• Vapi inbound gateway settings

• Phone number assignment

• Assistant assignment

If Voyced sends incoming calls through the registered contact but Vapi does not accept them, provide Vapi support with a SIP trace and the relevant registration details.

One-Way Audio

Check:

• RTP media ports

• SIP signalling and SDP addresses

• NAT configuration

• Audio codec negotiation

• Network access between the Vapi media server and Voyced

Final Tips

• Always use your Voyced SIP account credentials.

• Keep the SIP server set to sip.voyced.eu.

• Use Your-Voyced-DID as the authentication username.

• Use YourServicePassword as the SIP password.

• Configure the sipRegisterPlan when Voyced requires registration.

• Keep the inbound gateway disabled until the verified signalling addresses are available.

• Assign your Voyced number to the correct AI assistant.

• Test inbound and outbound calling separately.

• Never expose your Vapi private API key or live SIP password in screenshots or support logs.

Vapi supports custom SIP trunks with digest authentication and registration settings. Full inbound operation with Voyced's registration-based service must be confirmed through an actual connection test.

Last updated: 01/10/2026

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Given the fast evolution of the telecom sector, Voyced does not offer any guarantee about the accuracy and completeness of the information offered. 
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