91307: Could not connect to sink endpoint

Twilio records this error when Event Streams cannot establish a connection to your sink endpoint.

Because the connection could not be established, no event was sent. Twilio will automatically retry delivery per retry policy.

• The sink hostname could not be resolved via public DNS.
• The sink closed or reset the connection attempt because no service was listening on the designated port.
• A firewall, security group, or network access control list silently dropped Twilio's incoming connection request.
• The endpoint presented an expired, self-signed, hostname-mismatched, or incomplete SSL/TLS certificate chain.
• The sink hostname resolves to a private IP space or an unroutable endpoint that is unreachable over the public internet.

• Confirm that your sink's domain name is publicly resolvable and resolves to an accessible, public IP address.
• Ensure your target server presents a valid, unexpired SSL/TLS certificate issued by a trusted Certificate Authority (CA) that matches your configured domain name.
• Ensure your network firewalls, cloud security groups, or API gateways permit inbound traffic from Twilio's public IP ranges.
• Confirm that the protocol (https://) and port (default 443) configured in your sink setting match your receiving application's configuration.
• Run an external curl command or TLS verification check from a host outside your private network to isolate network reachability issues.

• 91300: Event delivery to sink failed
• 91308: Sink endpoint did not respond in time

• Event Streams overview
• Sink resource
• Subscription resource