Issue
When using Twilio Elastic SIP Trunking to perform PSTN call transfers, you may encounter outbound call failures with a 403 error and error code 32206:
"From number (caller ID) must be valid and not on the do-not-originate (DNO) list."
This article explains the causes of this error, recent regulatory changes affecting caller ID usage, and how to resolve or avoid this issue.
Symptoms
- Outbound PSTN call attempts via Elastic SIP Trunking are rejected.
- Error response: 403 Forbidden
- Twilio error code: 32206
- Error message: “From number (caller ID) must be valid and not on the do-not-originate (DNO) list.”
- Occurs even when using a Verified Caller ID or a Twilio-owned number.
Product
Programmable Voice
Environment
Twilio Console
Cause
This error occurs when the caller ID (the “From” number) used for the outbound call is either:
- Not a valid, recognized number in your Twilio account,
- On the industry-wide Do-Not-Originate (DNO) list, or
- Blocked due to regulatory restrictions.
Recent Regulatory Changes
-
Outbound calls from Indian numbers (+91) to other Indian PSTN destinations are no longer supported by Twilio as of August 1, 2024.
- This applies to all Twilio products, including Elastic SIP Trunking, <Dial>, and the Calls API.
- Calls using a +91 caller ID to another +91 destination will be blocked and return error 32206.
-
Transit Caller ID feature is being sunset.
- If you previously relied on this feature to forward the original caller ID, you must now use alternative methods (see below).
Resolution
1. Use a Valid Non-Indian Caller ID
- For calls to Indian PSTN destinations, use a non-Indian (non-+91) caller ID that is either:
- A Twilio-owned number in your account, or
- A Verified Caller ID in your account.
2. Immutable Call Forwarding with CallToken (Beta)
- If you need to forward the original inbound caller ID (e.g., for call transfers), enable the Immutable Call Forwarding feature with CallToken.
- This allows you to preserve the original caller ID when forwarding calls, provided you include the required X-Twilio-CallToken header in your SIP requests.
- Contact Twilio Support to request access to this feature if it is not already enabled on your account.
3. Check Your Trunk Configuration
- In the Twilio Console, navigate to Elastic SIP Trunking > Manage > Trunks > [Your Trunk] > General > Call Transfer (SIP Refer).
- Ensure your caller ID settings align with the above requirements.
Additional Information
If you encounter error 32206 when making outbound PSTN calls via Twilio Elastic SIP Trunking, review your caller ID configuration and ensure compliance with current regulatory requirements. Use a valid, non-Indian caller ID or enable Immutable Call Forwarding for dynamic caller ID preservation.
- Using an Indian caller ID for outbound calls to Indian destinations will result in failure due to regulatory restrictions, regardless of verification status.
- The DNO list is maintained to prevent call spoofing and fraud; numbers on this list cannot be used as caller IDs for outbound calls.
Below you will find references to useful documents:
For further assistance, please reach out to Twilio Support.