HTTP Retrieval Failure

What this error means

Root causes

How to fix it

1. 1

   Verify webhook URL accessibility

   Test your webhook URL directly by making a curl request from your server or a tool like Postman. Ensure the endpoint responds with a 200 status code. Use: curl -X GET 'https://yourdomain.com/your/webhook/path' -v. Check for any error messages or timeouts.

2. 2

   Check webhook configuration in Twilio Console

   Log into your Twilio Console, navigate to Phone Numbers > Manage Numbers > Select your number, and verify the webhook URL is correctly configured. Ensure it includes the full protocol (https://), domain, and path. Confirm it matches your actual endpoint exactly.

3. 3

   Verify DNS resolution

   Run 'nslookup yourdomain.com' or 'dig yourdomain.com' from your server to confirm DNS resolution works. If DNS fails, contact your domain registrar or DNS provider. Ensure your domain is pointing to the correct IP address.

4. 4

   Check firewall and security group rules

   Verify that your firewall, AWS Security Groups, Azure NSGs, or other network security controls allow inbound HTTPS traffic (port 443) on your webhook endpoint. Whitelist Twilio's IP ranges if you have IP-based restrictions. See https://www.twilio.com/en-us/changelog/twilio-ip-ranges for current Twilio IP addresses.

5. 5

   Validate SSL/TLS certificate

   If using HTTPS (required), ensure your SSL certificate is valid and not expired. Test with: openssl s_client -connect yourdomain.com:443. Look for certificate errors or expiration dates. Use tools like SSL Labs (https://www.ssllabs.com/ssltest/) to validate certificate chain.

6. 6

   Review application server logs

   Check your application server logs (Apache, Nginx, Node.js, etc.) for the time of the failed webhook delivery. Look for connection refused, timeout, or 5xx error messages. If you see no logs, the request never reached your server, indicating a network issue.

7. 7

   Ensure webhook handler responds quickly

   Verify your webhook endpoint responds within Twilio's timeout window (typically 5-10 seconds). Implement asynchronous processing if your webhook logic takes time. Return a 200 status code immediately and process call logic in a background queue. Slow endpoints may timeout and trigger 11200 errors.

8. 8

   Test with a public webhook testing tool

   Use a temporary public URL from services like ngrok, RequestBin, or Webhook.site to test webhook delivery. Update your Twilio webhook URL to point to one of these services, then trigger a call. This isolates whether the problem is network-related or application-specific.

9. 9

   Verify HTTP method and request format

   Ensure your webhook endpoint accepts POST requests (default for Twilio). Check your application framework's routing to confirm the method matches. Verify your code doesn't have strict content-type validation that rejects Twilio's request format.

10. 10

    Enable Twilio webhook request logging

    Use Twilio's monitoring and logging features in the Console under Debugger > Call Logs to see the exact error details. Click on a failed call to see the webhook failure reason, which may provide additional context about the root cause.

11. 11

    Implement exponential backoff and retry logic

    While Twilio handles retries on its end, ensure your application gracefully handles scenarios where webhooks fail. Implement monitoring to alert when webhook failures occur repeatedly. Consider using Twilio's webhook response codes to signal whether a request should be retried.

    // Node.js example: Proper webhook response
    app.post('/webhook', (req, res) => {
      try {
        // Process webhook
        res.status(200).send('OK'); // Return immediately
        
        // Handle call logic asynchronously
        processCallAsync(req.body).catch(err => console.error(err));
      } catch (error) {
        console.error('Webhook error:', error);
        res.status(500).send('Internal error'); // Signal retry
      }
    });

12. 12

    Monitor and alert on webhook failures

    Set up monitoring and alerting on webhook failures. Use Twilio's API to query call logs and detect 11200 errors in real-time. Configure PagerDuty, Datadog, or similar tools to alert your team immediately when webhook delivery fails.

Prevention

Prevent 11200 errors by implementing robust webhook infrastructure: use a reliable hosting provider with high uptime, configure automatic health checks and failover mechanisms, use content delivery networks (CDNs) or load balancers for redundancy, implement comprehensive application monitoring to detect crashes, maintain valid SSL certificates with renewal automation, test webhook endpoints regularly with synthetic monitoring, document your webhook URL and update it whenever infrastructure changes, implement request logging to track all incoming webhook attempts, and maintain fast response times (under 5 seconds) by offloading heavy processing to background jobs.