There was a network failure attempting to connect to this URL. Twilio will try for 10 seconds to establish a TCP connection to your URL (two 5-second attempts). Twilio will wait for a total of 15 seconds to receive an HTTP response. This includes the TCP connection time, so if it took six seconds to establish a TCP connection, your server would have 9 seconds to deliver an HTTP response. If either of those timers expire, we fail the request, fire a notification, and try your fallback URL, if one is specified.