No ACK was received from your SIP endpoint 32 seconds after sending a 200 OK response, which resulted in the termination of the Inbound call. As per RFC 3261, the calling device's SIP endpoint must send an ACK to acknowledge the receipt of a 200 OK response, to establish a successful call.
Possible Causes
Your NAT configuration may be incorrect.
Your Firewall may be blocking traffic.
SIP signaling not adhering to RFC 3261. For example ACK sent to the wrong IP address or using incorrect Route headers or Request URI.
A network disruption or packet loss within or between your network and the Twilio network may have caused the ACK messages to get lost.
Possible Solutions
Review configurations of your SIP endpoint. Consult your documentation for details.
Review logs on your SIP endpoint if possible. Consult your documentation for details on how to enable and access the logs.
SIP devices generally re-transmit messages multiple times, in the event a single message is lost. Ensure your device is configured with the maximum retransmissions.
Review proper SIP signaling by downloading PCAP via call log in Twilio console. And if possible, capture PCAP at your SIP endpoint to narrow down the cause of the signaling issue.