48004: Callback returned an error

This error occurs when Twilio Frontline sends a request to one of your configured callback URLs and your application returns an error response instead of completing successfully. It can affect the callback URLs you configure for Frontline features such as CRM lookups, outgoing conversations, templates, and custom routing.

• Your Frontline callback URL points to the wrong path, an outdated deployment, or another endpoint that returns an HTTP error response.
• Your callback endpoint starts handling the request but fails because of an application exception, dependency failure, or other server-side processing error.
• Your webhook validation or authentication logic rejects the request and returns 401 or 403, including cases where signature validation uses the wrong URL or modified request data.
• Your endpoint redirects the request to another URL, and the redirected request no longer reaches the handler you expected.

• In Frontline Console, review each configured callback URL and make sure it points to the correct public endpoint for the callback you are using. Check CRM, Outgoing Conversations, Templates, and Routing callbacks separately.
• Test the callback URL directly and confirm that your application returns a successful response instead of a 4xx or 5xx error. Use the Twilio Debugger to inspect the webhook request and response details.
• Review your application logs and fix any unhandled exceptions, failed downstream calls, or other server-side errors that occur while processing the callback.
• If you validate the X-Twilio-Signature header, validate it against the exact URL Twilio requested and the original request parameters or body so valid Frontline requests are not rejected.
• Remove unexpected HTTP redirects or URL rewrites so the callback request reaches your intended handler directly.

• Twilio Debugger
• Getting Started with Twilio Webhooks
• Webhooks security