Twilio error 11205 is distinct from 11200 in an important way: Twilio successfully established a TCP connection to your server, but the connection broke down before a complete HTTP response was received. This means your server is reachable and accepting connections, but something is causing the response to fail mid-flight, either due to a server-side timeout, an SSL negotiation failure after the TCP handshake, or the server closing the connection prematurely. Diagnosing 11205 requires looking at server-side behavior rather than network reachability.
What Causes This Error
The most frequent cause is a webhook handler that takes longer than Twilio's 15-second response timeout to return a response: Twilio will close the connection and log 11205 if your webhook has not sent at least the first byte of the HTTP response within 15 seconds of making the request. SSL certificate issues that occur after the TCP connection is established, such as a certificate that is valid for the domain but signed by a CA that is not in Twilio's trusted certificate store, cause the TLS handshake to fail after the TCP layer connects, which Twilio reports as 11205 rather than 11200. A web server that accepts the TCP connection (meaning the OS-level listen backlog has accepted it) but then crashes or runs out of worker threads before it can process the request will close the connection without sending any bytes, which also generates 11205. Misconfigured keep-alive settings or HTTP/2 protocol negotiation failures between Twilio's HTTP client and certain web server configurations are a less common but real cause of mid-connection failures.
How to Fix It Step by Step
Time your webhook handler by adding request logging that records the timestamp at the start and end of the handler function and compare this against Twilio's 15-second limit: any handler that consistently takes more than 10 seconds is at serious risk of triggering 11205. Refactor slow webhook handlers to respond immediately with a TwiML reply and then perform any expensive operations (database writes, external API calls, email sends) asynchronously in a background job queue, since Twilio only needs the TwiML response quickly and does not require your backend processing to complete first. Test your SSL certificate validity and chain completeness using the SSL Labs server test, which will flag issues like incomplete certificate chains, weak cipher suites, or root CA trust problems that can cause TLS failures on Twilio's client. For server thread exhaustion issues, review your web server's worker configuration (Gunicorn workers, Node.js cluster processes, or Apache/Nginx worker settings) and increase the worker count or switch to an asynchronous server model that can handle more concurrent connections without blocking.
How to Prevent It from Recurring
Set a strict internal timeout limit in your webhook handler code that is shorter than Twilio's 15-second limit: if your handler has not completed within 10 seconds, return a safe default TwiML response immediately and log the slow execution for offline investigation, rather than allowing the handler to continue and risk the 15-second cutoff. Deploy your webhook server behind a CDN or load balancer with TLS termination (such as AWS ALB, Cloudflare, or Nginx acting as a reverse proxy) that handles SSL using a well-known CA certificate and modern cipher suite configuration, removing the risk of obscure TLS compatibility issues between Twilio and your origin server. Monitor your webhook handler response time using application performance monitoring and set an alert threshold at 8 seconds so you are warned of slow handlers before they start hitting Twilio's timeout. Run regular SSL certificate expiry checks with an automated monitoring tool and configure renewal reminders at 30 days before expiry, ensuring your certificate is always current and Twilio's TLS validation always succeeds.
When to Call a Specialist
If your webhook handler returns quickly in local testing but consistently times out in production under load, you likely have a concurrency issue such as database connection pool exhaustion or a synchronous external API call that blocks under high traffic, and identifying the bottleneck requires profiling the production environment. A specialist can instrument your webhook handler with distributed tracing to identify which specific operation is consuming the most time under production load conditions, and recommend whether the fix is a connection pool increase, an async refactor, or a caching layer. You should also seek specialist help if your SSL configuration appears correct in tests but 11205 errors continue intermittently, as some SSL handshake failures are only triggered by specific cipher suite negotiations that depend on the TLS client version Twilio uses, which changes over time. Intermittent 11205 errors are among the most difficult webhook issues to reproduce and diagnose without specialist tooling.
Conclusion
Error 11205 is a mid-connection failure caused by handler timeouts or SSL negotiation problems, both of which are fixed on the server side with response time optimization and proper TLS configuration. 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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