Understanding Failed to Connect messages in xMatters logs (Voice Notifications)

Question

When looking through xMatters activity logs, I sometimes see errors like:

UNREACHABLE. The called party was unreachable, due to a 403 forbidden, 404 not found, 
or anything between 501 and 599

or call results such as:

Call queued in proxy
Failed to Connect. Call result: NO_ANSWER (408)
REJECTED

What do these messages mean?

Environment

• All versions of xMatters

• Voice notifications

Answer

These errors can be found in message delivery logs and are indicators of problems encountered by downstream telecommunications providers or at the handset/carrier level.

When an error is received from a provider, xMatters retries the call where appropriate. Often the error is temporary and the call is successful when retried.

Below is a list of common errors related to telephone calls and how to interpret them:

• 403 forbidden: The call was rejected by the receiver's network. This typically indicates that the call was not permitted to complete to the destination (for example, due to call blocking, number configuration, or policy) and is not usually related to the content of the notification.

• 404 not found: The user does not exist on the destination network. This often indicates that the called number is incorrect, no longer in service, or not routable from the carrier placing the call.

• 501-599: Errors in this category are less common and generally indicate a problem at the carrier or upstream provider level

• Call queued in proxy > Failed to Connect. Call result: NO_ANSWER (408): xMatters successfully queued the outbound call attempt with the voice provider, but the call timed out without being answered or reaching voicemail.

Call failures can also occur due to carrier-level spam or fraud blocking. In some cases, phone carriers may use anti-spam filters that prevent calls from going through, even when the number is correct and has worked previously.

Fix

If you experience persistent errors, you can also review the xMatters event or delivery logs to check whether voice providers failed to connect to the destination device, and collect multiple recent examples to share with support:

• Gather several failures that occurred within the last 24 hours (providers typically require recent samples to investigate).

• For each example, note the time of the call and what you observed (for example, whether the phone rang, reached voicemail, or appeared blocked).

If the issue persists after you have verified numbers, caller ID settings, and carrier behavior, please Submit a Request with xMatters Customer Support and include the sample call details so the issue can be escalated to the downstream carrier if needed.