Twilio error 11200 means Twilio attempted an HTTP request to your configured webhook URL and received no response at all: the TCP connection could not be established, the DNS lookup failed, or the server actively refused the connection. This error is logged in the Twilio Debugger and appears on every call or message event that Twilio tried to deliver to the unreachable URL. Because Twilio cannot proceed without a valid TwiML response, the call or message handling stops until you restore webhook reachability.
What Causes This Error
The most common cause is a web server that is down, crashed, or not yet started, meaning no process is listening on the port that your webhook URL points to. A second common cause is a firewall rule that blocks inbound HTTP or HTTPS traffic from Twilio's IP ranges: Twilio publishes its webhook source IP ranges in its documentation, and any firewall or security group that does not include those ranges will silently drop Twilio's connection attempts. A typo in the webhook URL configured in the Twilio Console, such as a missing path segment, an incorrect domain, or an HTTP vs HTTPS mismatch, is a third cause that results in an immediate connection refusal or DNS failure before Twilio's request can even be sent. Expired or incorrectly configured SSL certificates on your webhook server cause TLS handshake failures that manifest as 11200, since Twilio treats a failed TLS handshake as an HTTP retrieval failure.
How to Fix It Step by Step
Open the Twilio Console, navigate to Monitor, then Debugger, and find the most recent 11200 alert to retrieve the exact URL Twilio attempted and the timestamp of the failure, which gives you a precise starting point for diagnosis. Copy the webhook URL from the Debugger and paste it into a browser or run curl -v against it from a machine outside your network to confirm whether it is publicly reachable: if curl also fails, the problem is server-side or firewall-related rather than Twilio-specific. Check your web server process is running (for example, verify your Node.js, Django, or Rails process is alive and listening on the configured port) and confirm that your server's security group or firewall allows inbound HTTPS traffic from 0.0.0.0/0 or from Twilio's specific IP ranges. If the URL and server are correct but Twilio still cannot reach them, use a tunneling tool like ngrok to temporarily expose your local server to the public internet and substitute the ngrok HTTPS URL in your Twilio webhook configuration to confirm the TwiML logic works end-to-end while you resolve the production server access issue.
How to Prevent It from Recurring
Set up external uptime monitoring for your webhook endpoint using a monitoring service that checks the URL every minute from an external network and alerts your team immediately when it becomes unreachable, giving you notification before Twilio starts logging 11200 errors. Configure Twilio's built-in webhook fallback URL in the Console by navigating to the phone number settings and filling in the Fallback URL field with a secondary webhook endpoint that returns a safe default TwiML response, so that calls are not dropped entirely if your primary server is temporarily unavailable. Use a health check endpoint on your webhook server (a dedicated /health path that returns HTTP 200 quickly) and add it to your load balancer's health check configuration so that your load balancer automatically routes around unhealthy instances rather than sending Twilio's requests to a down server. Subscribe to Twilio Debugger alerts under Console, then Monitor, then Alerts so that 11200 errors generate an immediate notification to your on-call team rather than being discovered after the fact in log review.
When to Call a Specialist
If your server is confirmed running and publicly reachable from a browser or curl but Twilio still returns 11200, the issue may be a TLS configuration problem where your SSL certificate chain is incomplete or uses a cipher suite that Twilio's HTTP client does not support, and diagnosing this requires examining the TLS handshake at the packet level. A specialist can use tools like ssllabs.com's server test and Wireshark-level TLS inspection to identify exactly where the SSL handshake fails between Twilio's client and your server. You should also escalate if 11200 errors are intermittent and correlate with specific times of day, as this pattern often indicates a resource exhaustion issue (connection pool saturation, memory pressure, or a scheduled job that temporarily blocks the web server) that requires profiling to identify. Persistent 11200 errors on a production voice application that is handling live calls are an emergency that benefits from specialist rapid-response diagnosis.
Conclusion
Error 11200 is a connectivity failure between Twilio and your webhook server that is resolved by ensuring your endpoint is publicly reachable, SSL-valid, and not blocked by a firewall. If this error is blocking your production system, contact our team and we will diagnose and fix it within the hour.
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