Rejected INVITEs in US East

Update timeline

1. resolved Apr 23, 2026, 01:38 AM UTC

   Between 13:15 and 14:25 UTC on April 22, approximately 5% of inbound SIP calls routed through our US East region were rejected by our system due to a failing internal trunk lookup. Upstream carriers surfaced these rejections to end users as 503 "Service Unavailable" responses. A recent change to our internal service responsible for SIP trunk authorization lookups caused trunk queries to return empty results under certain conditions. When our SIP service received an empty trunk lookup, it rejected the inbound INVITE. The regression was deployed to one US region as part of a staged rollout. Our routine checks during the release identified the issue. Once the offending change was rolled back, inbound call rejections returned to baseline within minutes and full service was restored. Other regions and all outbound calls were unaffected. We are introducing a dedicated monitor for this specific failure mode so that any recurrence pages our on-call engineers immediately, rather than relying on broader error-rate signals.