Connect a Vapi BYOC SIP trunk to a DIDHub phone number

Vapi supports Bring-Your-Own-Carrier (BYOC) so you can use any SIP trunk — including DIDHub — instead of paying Vapi's bundled telecom markup. This tutorial walks through provisioning, registering, and binding a DID end-to-end.

Step 1: Create a SIP trunk in DIDHub

# Dashboard → SIP Trunks → New trunk
Name             : vapi-prod
Mode             : SIP digest auth
Username         : vapi_a8f3
Password         : "<auto-generated>"
Region           : us-east, eu-west (multi-region)
Codecs           : PCMU, OPUS
STIR/SHAKEN      : A-attestation
Inbound caller-id format : E.164

Step 2: Register the trunk in Vapi

Vapi dashboard → Phone Numbers → Import → SIP Trunk (BYOC):

curl -X POST https://api.vapi.ai/credential \
  -H "Authorization: Bearer $VAPI_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "provider": "byo-sip-trunk",
    "name": "didhub-prod",
    "gateways": [
      { "ip": "sip.didhub.io" }
    ],
    "outboundAuthenticationPlan": {
      "authUsername": "vapi_a8f3",
      "authPassword": "<PASSWORD>"
    },
    "outboundLeadingPlusEnabled": true,
    "techPrefix": null
  }'

Step 3: Import the DID

curl -X POST https://api.vapi.ai/phone-number \
  -H "Authorization: Bearer $VAPI_API_KEY" \
  -d '{
    "provider": "byo-phone-number",
    "name": "didhub-+15551234567",
    "number": "+15551234567",
    "credentialId": "<credential-id-from-step-2>",
    "assistantId": "<your-vapi-assistant-id>"
  }'

Step 4: Bind the DID in DIDHub to the trunk

Numbers → +1 555 123 4567 → Routing → SIP Trunk: vapi-prod. Save.

Step 5: Test inbound + outbound

Troubleshooting

• 403 on Vapi credential creation: verify $VAPI_API_KEY has the credentials:write scope.
• Inbound rings but assistant does not answer: assistantId on the phone-number record is required (or set squadId).
• Outbound 503: DIDHub trunk auth is wrong — double-check username/password from the trunk detail page.