Issue
When attempting to place an outbound call from Twilio Flex, the call fails and returns error 21216: “Number is blocked.” This error appears in the Flex UI and/or in your application logs.
Product
Twilio Flex
Environment
Twilio Console
Cause
Twilio blocks certain outbound calls before connecting them to the destination for one or more of the following reasons:
- The destination number is classified as high risk for fraud or abuse (e.g., toll fraud).
- Regulatory restrictions prevent calls to the destination.
- The account is attempting to call a
+1(US/Canada) destination without a valid Primary Customer Profile.- This can occur if:
- The account does not have a Primary Customer Profile.
- The account only has an Individual Customer Profile approved after October 2025 (these do not satisfy the requirement for +1 calling).
- This can occur if:
Resolution
- Confirm the Reason for the Block
- Review the error context in Debugger or Flex logs.
- Check if the destination is a high-risk or restricted number.
- Verify your account’s Customer Profile status in Trust Hub.
- If the Block Is in Error (Legitimate Business Use)
- If the destination is legitimate and you believe it is blocked in error, request a review by providing to our Support Team:
- The blocked destination number
- Your business use case for calling this number
- For +1 Destinations
- Ensure your account has a valid Primary Customer Profile in Trust Hub.
- If you only have an Individual Profile approved after October 2025, create and submit a Business Customer Profile for approval.
- Retry the call after the profile reaches “Twilio Approved” status.
- Review and Adjust Dialing Permissions
- In Console, review your Voice Dialing Geographic Permissions.
- Enable only the countries and number ranges you expect to call to reduce exposure to toll fraud.
- Application Best Practices
- Validate destination numbers in your application.
- Rate-limit outbound call requests to avoid triggering fraud controls.